Mask blank, phase-shift mask and method for manufacturing semiconductor device

ABSTRACT

To provide a phase-shift mask in which the reduction in thickness of a light-shielding film is provided when a transition metal silicide-based material is used for the light-shielding film and by which the problem of ArF light fastness can be solved; and a mask blank for manufacturing the phase-shift mask. 
     A mask blank has a structure in which a phase-shift film, an etching stopper film, a light-shielding film, and a hard mask film are laminated in said order on a transparent substrate, and at least one layer in the light-shielding film is made of a material which contains transition metal and silicon, and satisfies the conditions of Formula (1) below: 
         C   N ≤9.0×10 −6   ×R   M   4 −1.65×10 −4   ×R   M   3 −7.718×10 −2   ×R   M   2 +3.611× R   M −21.084   Formula ( 1 )
 
     wherein R M  is a ratio of the content of transition metal to the total content of transition metal and silicon in said one layer, and C N  is the content of nitrogen in said one layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Divisional of application Ser. No. 15/121,124 filed Aug. 24,2016, claiming priority based on International Application No.PCT/JP2014/082500 filed Dec. 9, 2014, claiming priority based onJapanese Patent Application No. 2014-055099 filed Mar. 18, 2014, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a mask blank, a phase-shift mask, and amethod for manufacturing a semiconductor device.

BACKGROUND ART

In a manufacturing process of a semiconductor device, a fine pattern isgenerally formed using a photolithographic method. In the formation ofthe fine pattern, multiple substrates, which are referred to as transfermasks, are usually used. The transfer mask is formed by providing thefine pattern comprised of a metal thin film, etc. on a generallytransparent glass substrate. The photolithographic method is also usedin the manufacture of the transfer mask.

Refinement of a pattern for the semiconductor device requires therefinement of a mask pattern formed in the transfer mask as well asshortening of a wavelength of an exposure light source used inphotolithography. Nowadays, the exposure light sources used in themanufacture of semiconductor devices are shifting from KrF excimerlasers (wavelength: 248 nm) to ArF excimer lasers (wavelength: 193 nm),that is, shorter wavelength light sources are increasingly used.

The known types of transfer masks include a binary mask including alight-shielding film pattern made of a chromium-based material on aconventional transparent substrate, as well as a half tone phase-shiftmask. The half tone phase-shift mask comprises a phase-shift filmpattern on the transparent substrate. The phase-shift film has functionsfor allowing transmission of light at an intensity not substantiallycontributing to the light exposure and for providing the lighttransmitted through the phase-shift film with a predetermined phasedifference with respect to light traveling the same distance throughair, thereby generating a so-called phase-shift effect.

Generally, in the transfer mask, a periphery region outside the regionin which a transfer pattern is formed should ensure optical density (OD)not less than a predetermined value such that, upon the exposuretransfer to a resist film on a semiconductor wafer using an exposureapparatus, the resist film will not be affected by the exposure lighttransmitted through the periphery region. Usually, in the peripheryregion of the transfer mask, OD is desirably 3 or more, and at leastabout 2.7 of OD is required. However, the phase-shift film of the halftone phase-shift mask has a function for allowing the transmission ofthe exposure light at a predetermined transmittance, and thus, it isdifficult to ensure the optical density required for the peripheryregion of the transfer mask by this phase-shift film alone. Therefore, alight-shielding film (light blocking film) is laminated onto asemitransparent film having predetermined phase-shift amount andtransmittance with respect to the exposure light, so that a laminatedstructure of the semitransparent film and light-shielding film ensuresthe predetermined optical density.

On the other hand, the use of a transition metal silicide-based materialfor the light-shielding film to increase the accuracy in formation of afine pattern in the light-shielding film has been considered in recentyears. Patent Document 1 discloses the relevant technique.

However, it has been recently ascertained that a MoSi-based (transitionmetal silicide-based) film, when irradiated with ArF excimer laserexposure light (ArF exposure light) for a long time, causes a phenomenonof pattern line width variation, which is also regarded as a problem inPatent Documents 2 and 3, etc. Regarding this problem, Patent Document 2discloses that the formation of a passive film on a surface of a patternformed of a MoSi-based film improves light fastness to the ArF exposurelight (ArF light fastness), and Patent Document 3 discloses thetechnique to improve the ArF light fastness by providing theconstitution in which a transition metal silicon-based material filmsuch as a half tone phase-shift film has the oxygen content of 3 at % ormore, and has the silicone content and transition metal content within arange satisfying a predetermined relational expression, and in which asurface oxide layer is provided on a surface layer of the transitionmetal silicon-based material film.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Publication 2007-241065

Patent Document 2: Japanese Patent Application Publication 2010-217514

Patent Document 3: Japanese Patent Application Publication 2012-058593

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Patent Document 1 describes the use of a transition metal silicide-basedmaterial for a phase-shift film or light-shielding film. However, as fora material used for the phase-shift film and light-shielding film,Patent Document 1 does not take the viewpoint of ArF light fastness intoconsideration. In Patent Document 2, although the ArF light fastness isimproved by forming a passive film on a surface of a pattern formed of aMoSi-based film, this approach does not change an inner structure of theMoSi-based film. That is, the inner structure of the MoSi-based film hasthe ArF light fastness equivalent to a conventional one. Thus, a passivefilm should be formed not only on a surface layer of an upper surface inthe pattern of the MoSi-based film, but also on surface layers of sidewalls. In Patent Document 2, while a passive film is formed byperforming plasma treatment, UV irradiation treatment, or heat treatmentafter forming the pattern in the MoSi-based film, the pattern formed inthe MoSi-based film has a large difference in density in a plane, andthe distance between side walls of adjacent patterns is often extremelydifferent. Therefore, there is a problem that it is not easy to formpassive films all having the same thickness on the side walls of all thepatterns.

On the other hand, Patent Document 3 shows one solution for the ArFlight fastness in using the transition metal silicide-based materialfilm. As for the transition metal silicide-based material, it has beenconfirmed by the experiment by the applicant that the ArF light fastnesstends to be obtained by increasing the nitrogen content (FIG. 2illustrated in the Embodiments section). That is, by using thetransition metal silicide-based material film having the nitrogencontent equal to or greater than a predetermined amount for thephase-shift film or light-shielding film of the half tone phase-shiftmask, it can be expected to possess the ArF light fastness whileincreasing the accuracy in the formation of a fine pattern.

Patent Document 3 describes a mask blank having a structure in which ahalf tone phase-shift film and a light-shielding film are laminated insaid order on a transparent substrate. In Patent Document 3, the halftone phase-shift film is made of a transition metal silicon-basedmaterial which is comprised of a material containing transition metal,silicon, oxygen, and nitrogen, and the material composition applied isregarded as having high ArF light fastness in Patent Document 3. PatentDocument 3 discloses that the film made of the transition metalsilicon-based material regarded as having high ArF light fastness isused as a light-shielding film (laminated on the half tone phase-shiftfilm). As for the other materials used for the light-shielding filmlaminated on the half tone phase-shift film, it only describes amaterial containing chromium (chromium-based material), which has beenconventionally and broadly used. That is, Patent Document 3 onlydiscloses that the light-shielding film is made of a material having thehigh ArF light fastness.

Formation of the light-shielding film to be provided on the half tonephase-shift film (hereinafter also simply referred to as “phase-shiftfilm”) from the chromium-based material is the simplest approach sincethe ArF light fastness does not have to be taken into account. However,in view of the necessity to form a fine pattern in the light-shieldingfilm, the chromium-based material is not necessarily a preferablematerial. In the half tone phase-shift mask (hereinafter also simplyreferred to as “phase-shift mask”), a transfer pattern including thefine pattern is provided in the phase-shift film. The light-shieldingfilm is provided with a relatively sparse pattern such as alight-shielding band. The mask blank used for manufacturing thephase-shift mask generally has a structure in which a phase-shift filmand a light-shielding film are laminated from the transparent substrateside.

In the process for manufacturing the phase-shift mask from the maskblank, the transfer pattern to be formed in the phase-shift film shouldbe first formed in the light-shielding film by dry etching, such thatthe light-shielding film with the transfer pattern formed therein isused as an etching mask to form the transfer pattern in the phase-shiftfilm by the dry etching. Since the fine pattern is temporarily formed inthe light-shielding film, a material which can form the fine patternwith high accuracy is desirably used for the light-shielding film.

The light-shielding film made of the chromium-based material should bepatterned by the dry etching with a mixed gas of a chlorine-based gasand an oxygen gas. In the dry etching with the mixed gas of thechlorine-based gas and oxygen gas, it is difficult to increase thetendency of anisotropic etching due to characteristics of the etchinggas. Thus, it is not easy to increase the shape accuracy of pattern sidewalls, and it is also not easy to reduce CD accuracy variation in aplane (planar view). The accuracy of the transfer pattern formed in thislight-shielding film affects the accuracy of the transfer pattern in thephase-shift film formed by dry etching the phase-shift film.

A resist film made of an organic material tends to be vulnerable tooxygen plasma. In order to form a pattern in the light-shielding filmmade of the chromium-based material by the dry etching using the resistfilm as an etching mask, a thickness of the resist film should beincreased. Since the film thickness sufficient to ensure thepredetermined optical density is necessary due to the characteristics ofthe light-shielding film, the thickness of the resist film should becorrespondingly increased. When the thickness of the resist film isincreased, and the fine pattern is formed in the resist film, a patternaspect ratio (a ratio of width to height of the pattern) becomes high,and the resist pattern is liable to collapse, which is unfavorable forthe formation of the fine pattern. In view of the above, under theexisting circumstances, there are limitations in increasing the accuracywhen forming the fine pattern in the light-shielding film made of thechromium-based material.

If the light-shielding film is made of the transition metalsilicide-based material, the light-shielding film is patterned by thedry etching with a fluorine-based gas. Since the dry etching with thefluorine-based gas has a high tendency toward the anisotropic etching,it may increase the shape accuracy of pattern side walls. As disclosedin Patent Document 1, an etching mask used in patterning thelight-shielding film is often an etching mask film made of thechromium-based material, not the resist film made of the organicmaterial. Further, since both the phase-shift film and light-shieldingfilm are made of the transition metal silicide-based material, anetching stopper film made of the chromium-based material is oftenprovided between the phase-shift film and light-shielding film.

In addition, while not considered in Patent Document 1, in themanufacture of a phase-shift mask from the mask blank having such alaminated structure, if a mark such as an alignment mark outside theregion where the transfer pattern is formed is comprised of thelaminated structure of the light-shielding film and phase-shift film (analignment mark pattern is formed in the light-shielding film andphase-shift film such that the mark is identified by the contrastbetween the portion of the laminated structure of the light-shieldingfilm and phase-shift film and the portion where the transparentsubstrate is exposed), the etching mask film should remain after thecompletion of the dry etching for forming the transfer pattern in theetching stopper film, as described below.

Thus, the thickness and composition of the etching mask film and etchingstopper film should be designed such that the etching time required forthe dry etching for forming a pattern in the etching mask film is longerthan the etching time required for the dry etching for forming thepattern in the etching stopper film. In any of the design approaches,the thickness of the resist film tends to be increased compared to thefilm design without consideration for the formation of this alignmentmark.

If the transfer pattern is formed by dry etching the light-shieldingfilm using the etching mask film as a mask, the etching mask film madeof the chromium-based material has etching durability to thefluorine-based gas, but it does not mean that it remains completelyunetched. During the patterning of the light-shielding film, since asurface of the etching mask film is continuously exposed to the etchinggas with high anisotropy (biased etching gas), it is gradually etchedthrough a physical action, etc. Thus, the thickness of the etching maskfilm should be determined in view of a reduction amount of filmthickness during the dry etching with the fluorine-based gas for thepatterning of the light-shielding film, as well as a reduction amount offilm thickness during the dry etching with the mixed gas of thechlorine-based gas and oxygen gas for the patterning of the etchingstopper film.

When the thickness of the etching mask film is increased, the thicknessof the resist film used as a mask in patterning the etching mask filmshould also be increased. Therefore, there is a need for the etchingmask film having a reduced thickness. In order to reduce the thicknessof the etching mask film, the thickness of the light-shielding film isdesirably reduced. However, the light-shielding film has a restrictionthat the predetermined optical density (OD) should be ensured. In orderto reduce the film thickness while possessing a “light-shielding”ability that is an original function of the light-shielding film, itsmaterial should have high optical density (OD) per unit film thickness.In the transition metal silicon-based material, the content of elementsother than the transition metal silicide should be decreased in order toincrease the optical density (OD) per unit film thickness. Inparticular, since the elements which cause the reduction in opticaldensity are oxygen and nitrogen, the content of these elements should bedecreased. However, from the viewpoint of the ArF light fastness, thenitrogen content should be equal to or greater than the predeterminedamount as described above. In this respect, an inevitable trade-off hasbeen considered to exist.

In view of the above, it is an object of the present invention toprovide a phase-shift mask in which the reduction in thickness of thelight-shielding film is provided even if the transition metalsilicide-based material is used to enable the formation of a finepattern in the light-shielding film and by which the problem of ArFlight fastness can be solved; a mask blank for manufacturing thephase-shift mask; and a method for manufacturing a semiconductor device.Means of Solving the Problems

In order to solve the above problems, the present invention comprisesthe following configurations.

(Configuration 1)

A mask blank having a structure in which a phase-shift film, an etchingstopper film, and a light-shielding film are laminated in said order ona transparent substrate,

wherein the etching stopper film is made of a material containingchromium;

wherein the phase-shift film is made of a material in which transitionmetal, silicon, and nitrogen are contained, and a ratio of the content[atom %] of transition metal to the total content [atom %] of transitionmetal and silicon is less than 4 [%];

wherein the light-shielding film has a single layer structure, or alaminated structure comprised of multiple layers; and

wherein at least one layer in the light-shielding film is made of amaterial which contains transition metal and silicon, but does notcontain nitrogen and oxygen, or a material which contains transitionmetal, silicon, and nitrogen, and satisfies the conditions of Formula(1) below:

C _(N)≤9.0×10⁻⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³−7.718×10⁻² ×R _(M)²+3.611×R _(M)−21.084   Formula (1)

wherein R_(M) is a ratio [%] of the content [atom %] of transition metalto the total content [atom %] of transition metal and silicon in saidone layer, and C_(N) [atom %] is the content [atom %] of nitrogen insaid one layer.

(Configuration 2)

A mask blank having a structure in which a phase-shift film, an etchingstopper film, and a light-shielding film are laminated in said order ona transparent substrate,

wherein the etching stopper film is made of a material containingchromium;

wherein the phase-shift film is comprised of a surface layer and layersother than the surface layer;

wherein the layers other than the surface layer are made of a materialin which transition metal, silicon, and nitrogen are contained, a ratioof the content [atom %] of transition metal to the total content [atom%] of transition metal and silicon is less than 9 [%], and incompletenitride is a main component;

wherein the light-shielding film has a single layer structure, or alaminated structure comprised of multiple layers; and

wherein at least one layer in the light-shielding film is made of amaterial which contains transition metal and silicon, but does notcontain nitrogen and oxygen, or a material which contains transitionmetal, silicon, and nitrogen, and satisfies the conditions of Formula(1) below:

C _(N)≤9.0×10⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³−7.718×10² ×R _(M) ²+3.611×R_(M)−21.084   Formula (1)

wherein R_(M) is a ratio [%] of the content [atom %] of transition metalto the total content [atom %] of transition metal and silicon in saidone layer, and C_(N) [atom %] is the content [atom %] of nitrogen insaid one layer.

(Configuration 3)

A mask blank having a structure in which a phase-shift film, an etchingstopper film, and a light-shielding film are laminated in said order ona transparent substrate,

wherein the etching stopper film is made of a material containingchromium;

-   wherein the phase-shift film is comprised of a surface layer and    layers other than the surface layer;

wherein the layers other than the surface layer are made of a materialconsisting of silicon and nitrogen, or a material consisting of silicon,nitrogen, and one or more elements selected from metalloid elements,non-metallic elements, and noble gases;

wherein the light-shielding film has a single layer structure, or alaminated structure comprised of multiple layers; and

wherein at least one layer in the light-shielding film is made of amaterial which contains transition metal and silicon, but does notcontain nitrogen and oxygen, or a material which contains transitionmetal, silicon, and nitrogen, and satisfies the conditions of Formula(1) below:

C _(N)≤9.0×10⁻⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³−7.718×10² ×R _(M)²+3.611×R _(M)−21.084   Formula (1)

wherein R_(M) is a ratio [%] of the content [atom %] of transition metalto the total content [atom %] of transition metal and silicon in saidone layer, and C_(N) [atom %] is the content [atom %] of nitrogen insaid one layer.

(Configuration 4)

The mask blank according to Configuration 3, wherein the layers otherthan the surface layer in the phase-shift film have a structure in whicha low-transmittance layer and a high-transmittance layer are laminated,and

wherein the low-transmittance layer has nitrogen content that isrelatively lower than the high-transmittance layer.

(Configuration 5)

The mask blank according to Configuration 3 or 4, wherein the surfacelayer in the phase-shift film is made of a material consisting ofsilicon, nitrogen, and oxygen, or a material consisting of silicon,nitrogen, oxygen, and one or more elements selected from metalloidelements, non-metallic elements, and noble gases.

(Configuration 6)

The mask blank according to any one of Configurations 1 to 5, whereinthe optical density with respect to ArF excimer laser light is 2.7 ormore in the laminated structure of the phase-shift film, etching stopperfilm, and light-shielding film.

(Configuration 7)

The mask blank according to any one of Configurations 1 to 6, wherein ahard mask film made of a material containing chromium is provided on thelight-shielding film.

(Configuration 8)

A phase-shift mask manufactured from the mask blank according to any oneof Configurations 1 to 7.

(Configuration 9)

A method for manufacturing a semiconductor device, comprising the stepof: setting the phase-shift mask according to Configuration 8 on anexposure apparatus having an exposure light source for emitting ArFexcimer laser light, so as to transfer a transfer pattern onto a resistfilm formed on a transfer target substrate.

Effect of the Invention

According to a mask blank (and a phase-shift mask manufacturedtherefrom) of the present invention, even if the transition metalsilicide-based material is used for the light-shielding film, thethickness of the light-shielding film may be reduced, and it is possibleto solve the problem of ArF light fastness. Further, according to amethod for manufacturing a semiconductor device of the presentinvention, even if the phase-shift mask is used for a prolonged period(even if it is irradiated with the ArF excimer laser exposure light fora prolonged period) in the manufacture of the semiconductor device, theoccurrence of the phenomenon of pattern line width variation may berestrained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a layered configuration of amask blank according to Embodiment 1 of the present invention.

FIG. 2 is a graph showing the relationship between Mo/(Mo+Si) ratio andnitrogen content in each transition metal silicide-based material inwhich optical density per unit film thickness is a predetermined value(in a range of 0.060 [OD/nm] to 0.080 [OD/nm] in increments of 0.005).

FIGS. 3(a) to 3(h) are cross-sectional views showing a manufacturingprocess of a phase-shift mask according to Embodiment 1 of the presentinvention.

FIG. 4 is a cross-sectional view showing a layered configuration of amask blank according to a variant of Embodiment 3 of the presentinvention.

FIG. 5 is a schematic view for illustrating film formation modes when athin film is formed by reactive sputtering.

MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are specifically described belowwith reference to the drawings. Each of the embodiments below showsmerely one configuration for embodying the present invention, and it isnot intended to limit the present invention to its extent.

Regarding a phase-shift mask having a structure in which a phase-shiftpattern and a light-shielding band pattern are laminated on atransparent substrate in said order from the transparent substrate side,if it is intended to form both a phase-shift film and a light-shieldingfilm from a transition metal silicide-based material, a common design isto apply the transition metal silicide-based material having ArF lightfastness to both the phase-shift film and light-shielding film. However,as a result of earnest study by the inventors, it was found that thereis no practical problem even if the transition metal silicide-basedmaterial regarded as having low ArF light fastness is applied to thelight-shielding film.

When a phase-shift mask is set on a mask stage of an exposure apparatusfor the exposure transfer to a transfer target object (such as a resistfilm on a semiconductor wafer), the exposure light is generally incidentfrom a back side (main surface on which a phase-shift pattern is notprovided) of the transparent substrate of the phase-shift mask. Theexposure light incident on the transparent substrate is then incident onthe phase-shift film (phase-shift pattern) from the opposite mainsurface. The amount of exposure light is decreased during passagethrough the phase-shift film, such that the amount corresponds to apredetermined transmittance when the light exits from a surface of thephase-shift film. In a region where the light-shielding film exists onthe phase-shift film (a region where a light-shielding pattern exists),the exposure light decreased to the light amount corresponding to thepredetermined transmittance (if the etching stopper film is interposedbetween the phase-shift film and the light-shielding film, the exposurelight further passed through the etching stopper film) will be incidenton the light-shielding film.

The inventors discovered that the pattern line width variation caused byirradiating a thin film pattern made of the transition metalsilicide-based material with the ArF exposure light correlates with anaccumulated radiation value of the ArF exposure light. As describedabove, in comparison to a radiation value of the ArF exposure lightreceived by the phase-shift pattern of the phase-shift mask by singleexposure transfer to a transfer target object, the radiation value ofthe ArF exposure light received by the light-shielding pattern issignificantly smaller. That is, when the exposure transfer is performedon the phase-shift mask a predetermined number of times, the accumulatedradiation value of the ArF exposure light received by thelight-shielding pattern is significantly smaller than the accumulatedradiation value of the ArF exposure light received by the phase-shiftpattern.

Thus, when the exposure transfer to a transfer target object isperformed in a phase-shift mask having a structure in which aphase-shift pattern and a light-shielding pattern made of a transitionmetal silicide-based material with low ArF light fastness are laminatedon a transparent substrate, the number of times of use (number of timesof exposure transfer to the transfer target object) until thelight-shielding pattern line width changes to an unacceptable width issignificantly greater than in the case of exposure transfer to thetransfer target object performed under the same conditions in a transfermask comprising a light-shielding pattern without another interposedfilm on the transparent substrate.

A factor affecting the life of the phase-shift mask is not only theincrease in pattern line width relevant to the ArF light fastness. Forexample, the phase-shift mask must be cleaned with chemicals after it isused a predetermined number of times. During cleaning, a pattern surfaceof the phase-shift film or light-shielding film dissolves due to thechemicals, though only gradually (reduction of film thickness occurs).When the optical characteristics as the phase-shift film orlight-shielding film of the phase-shift mask become unsatisfied due tothe reduction of film thickness caused by repeated cleaning, thephase-shift mask reaches its end of life. There are other factorsaffecting the life of the phase-shift mask (the number of times that itcan be used). If the amount of line width variation of thelight-shielding film due to the ArF exposure is within an acceptablerange until the phase-shift mask reaches its end of life partlydetermined by these factors, there is no problem with the performance asa light-shielding film.

As a result of the above described earnest study, the inventors foundthat, in a light-shielding film laminated on the transparent substratewith an interposed phase-shift film that decreases the ArF exposurelight to the predetermined transmittance, even if the transition metalsilicide-based material is selected without considering the ArF lightfastness, the amount of line width variation of the light-shielding filmdue to the ArF exposure is within the acceptable range at least untilthe phase-shift film reaches its end of life, and there is substantiallyno problem with the ArF light fastness. Further, they reached theconclusion that the selection of a material forming the light-shieldingfilm from the viewpoint of a light-shielding performance that is afunction originally required for the light-shielding film results in amask blank in which a fine pattern can be formed in the phase-shiftfilm.

While the actual condition is that when using a transition metalsilicide-based material in response to a demand for the formation of afine pattern in a light-shielding film, an unsolvable trade-offrelationship as described above is believed to exist between

“a requirement that a material having high optical density per unit filmthickness (=as for the transition metal silicide-based material, amaterial having low content of oxygen and nitrogen) is necessary basedon the demand for the thinned thickness and light-shielding performancerequired for the light-shielding film” and

“the recent finding that the high light fastness to the ArF excimerlaser exposure light is required (=transition metal silicide containinga predetermined amount or more of nitrogen must be used)”,

the present invention provides a mask blank in which a material havinghigh optical density per unit film thickness (=transition metal silicidehaving low content of oxygen and nitrogen) is used for a light-shieldingfilm; a phase-shift mask; and a method for manufacturing a semiconductordevice, since the above finding has been derived for the first time bythe applicant.

Embodiment 1

FIG. 1 is a cross-sectional view showing a layered configuration of amask blank 10 according to Embodiment 1 of the present invention. Themask blank 10 of the present invention shown in FIG. 1 has a structurein which a phase-shift film 2, an etching stopper film 3, alight-shielding film 4, and a hard mask film 5 are laminated in saidorder on a transparent substrate 1.

Respective layers are described below.

<<Transparent Substrate>>

There is no particular limitation on the transparent substrate 1,provided that it is transparent to the ArF excimer laser. In the presentinvention, a synthetic quartz substrate, and various other glasssubstrates (e.g., soda lime glass, aluminosilicate glass, etc.) may beused. Among the various glass substrates, the synthetic quartz substratehas particularly high transparency at a wavelength of the ArF excimerlasers or in a shorter wavelength range, and thus, it is suitable as asubstrate for the mask blank of the present invention used in forming ahigh-definition transfer pattern.

<<Phase-Shift Film>>

The phase-shift film 2 allows the transmission of light at an intensitynot substantially contributing to the light exposure (e.g., 1% to 30%,preferably 2% to 20%, with respect to the exposure wavelength), and hasa predetermined phase difference (e.g., 150 degrees to 180 degrees).Specifically, the phase-shift film 2 is patterned so as to form aportion where the phase-shift film is left and a portion where nophase-shift film is left, such that a phase of light transmitted throughthe phase-shift film (light at an intensity not substantiallycontributing to the light exposure) is in a substantially invertedrelation with respect to a phase of light transmitted through theportion where no phase-shift film is left (ArF excimer laser exposurelight). In this way, the light transmitted through the portion where thephase-shift film is left and the light transmitted through the portionwhere no phase-shift film is left enter the other's region due to adiffraction phenomenon, thereby annihilating both of them, so that alight intensity at the boundary between the two portions is nearly zero,and a contrast, i.e., a resolution, at the boundary is improved. Thethickness of the phase-shift film 2 is preferably 70 nm or less.

If NTD (Negative Tone Development) process is used as anexposure/development process for a resist film on a wafer, a brightfield mask (transfer mask with a high pattern opening ratio) is used. Ina bright field phase-shift mask, when the transmittance of thephase-shift film is higher, the balance between 0-order light and firstorder light for the light transmitted through a transparent portion isbetter, thereby improving a pattern resolution on the resist film. It isbecause there is a greater effect that the exposure light transmittedthrough the phase-shift film interferes with the 0-order light toattenuate the light intensity. When the phase-shift film 2 is applied tothe bright field phase-shift mask, the transmittance at an exposurewavelength in the phase-shift film 2 is more preferably 10% or more.Also in this case, the transmittance at an exposure wavelength in thephase-shift film 2 is preferably 30% or less, and more preferably 20% orless.

The phase-shift film 2 is made of a material containing transitionmetal, silicon, and nitrogen. In this case, the transition metalincludes one or more metals of molybdenum (Mo), tantalum (Ta), tungsten(W), titanium (Ti), chromium (Cr), hafnium (Hf), nickel (Ni), vanadium(V), zirconium (Zr), ruthenium (Ru), rhodium (Rh), niobium (Nb), indium(In), tin (Sn), and palladium (Pd), etc., or alloys of these metals. Inaddition to the above elements, the material of the phase-shift film 2may contain elements such as nitrogen (N), oxygen (O), carbon (C),hydrogen (H), and boron (B). Further, the material of the phase-shiftfilm 2 may contain an inert gas, such as helium (He), argon (Ar),krypton (Kr), and xenon (Xe).

These materials have a high etching rate in the dry etching with anetching gas containing a fluorine-based gas, and thus, help to obtainvarious properties required for the phase-shift film. In particular,these materials are desirable as materials forming a phase-shift filmwhich should strictly control the phase of the exposure lighttransmitted through the phase-shift film. In the phase-shift film 2, apercentage [%] calculated by dividing the content [at % (atomicpercent)] of transition metal (M) in the film by the total content [atom%] of transition metal (M) and silicon (Si) (hereinafter referred to asM/M+Si ratio) is preferably less than 4 [%]. The M/(M+Si) ratio in thephase-shift film 2 is more preferably 3 [%] or less, and furtherpreferably 2 [%] or less.

The pattern line width variation in the thin film (phase-shift film 2)made of the transition metal silicide-based material which is caused bythe irradiation of the ArF exposure light is due to a phenomenon inwhich an altered layer containing Si and O as well as some amount oftransition metal is formed on a surface layer side of the pattern. Inthe thin film of the transition metal silicide-based material which isformed by the sputtering method, a structural gap is easily formed.Oxygen or water in the atmosphere easily enters the structural gap. Whenthe phase-shift film in such a state is irradiated with the ArF exposurelight, ozone is generated from oxygen or water in the thin film. Siliconor transition metal in a thin film receiving the irradiation of the ArFexposure light is excited, such that it couples with ozone to generateoxide of silicon or transition metal. The oxide of transition metal ischaracterized in that it spreads throughout the thin film so as to beeasily deposited on a surface layer. Further, due to the deposition ofthe oxidized transition metal onto a surface of the thin film, oxygen orwater in the atmosphere can more easily enter the thin film, therebypromoting further oxidation of silicon or transition metal in the thinfilm. That is, when the abundance ratio of transition metal in the thinfilm is high, the ArF light fastness is easily lowered.

If the M/(M+Si) ratio in the phase-shift film 2 is 4 [%] or more, analtered layer on a pattern surface layer of the phase-shift film 2,which is due to the deposition of transition metal upon irradiation withthe ArF exposure light, rapidly grows, and thus, the life of thephase-shift mask resulting therefrom tends to be shorter than the lifeof the phase-shift mask which is determined by factors other than thefactor relevant to the irradiation of the ArF exposure light. TheM/(M+Si) ratio set to be less than 4 [%] allows for the ArF lightfastness sufficient to be used as the phase-shift mask 20. However, theM/(M+Si) ratio in the phase-shift film 2 is preferably 1 [%] or more. Itis because when a phase-shift mask is manufactured from a mask blank,and a black defect present in a pattern in the phase-shift film 2 iscorrected by electron beam irradiation and an unexcited gas such asXeF₂, the phase-shift film 2 preferably has lower sheet resistance.

A surface layer of the phase-shift film 2 which is adjacent to theetching stopper film 3 preferably contains much oxygen relative to theoxygen content in the phase-shift film 2 other than the surface layer.By configuring the surface layer in this way, when the etching stopperfilm 3 is removed by the dry etching, the surface layer of thephase-shift film 2 may have high durability to the exposure to anetching gas that is a mixed gas of a chlorine-based gas and an oxygengas. A method for forming a surface layer in the phase-shift film 2 tohave the relatively high oxygen content includes a method foroxidatively treating the surface layer of the phase-shift film 2 afterits formation, a method for forming a layer from a material with thehigh oxygen content on a surface of the phase-shift film 2 by asputtering method, etc. The oxidation treatment which can be appliedincludes a heat treatment in a gas containing oxygen (such as in theatmosphere), or a treatment for oxidizing the surface layer by the flashirradiation using, for example, a flash lamp.

<<Etching Stopper Film>>

The etching stopper film 3 is made of a material containing chromium soas to ensure etching selectivity in relation to the light-shielding film4 and phase-shift film 2 in the dry etching for the patterning to form atransfer pattern. A material for the etching stopper film 3 may contain,in addition to the above-described elements, one or more elementsselected from nitrogen (N), oxygen (O), carbon (C), hydrogen (H), andboron (B). Further, in order to improve an etching rate in the dryetching with the chlorine-based gas and oxygen gas, and to enhancedurability to the dry etching with the fluorine-based gas, the materialfor the etching stopper film 3 may contain one or more elements selectedfrom indium (In) and tin (Sn). Moreover, the material for the etchingstopper film 3 may contain an inert gas, such as helium (He), argon(Ar), krypton (Kr), and xenon (Xe). Specifically, the material includes,for example, CrN, CrON, CrOC, and CrOCN.

The thickness of the etching stopper film 3 is preferably 3 nm or more,and more preferably 4 nm or more. Also, the thickness of the etchingstopper film 3 is preferably 10 nm or less, and more preferably 8 nm orless.

<<Light-Shielding Film>>

As explained above, in most cases, a phase-shift mask manufactured froma mask blank does not include the fine pattern in the light-shieldingfilm 4. However, in order to form the fine pattern in the phase-shiftfilm with great accuracy, it is necessary to enable the fine pattern tobe formed in the light-shielding film 4. For at least one layer in thelight-shielding film 4, the transition metal silicide-based material isused to enable the formation of the fine pattern, and a material havinghigh optical density per unit film thickness is used for thinning thefilm. In particular, at least one layer in the light-shielding film 4 ismade of a material which contains transition metal and silicon, but doesnot contain nitrogen and oxygen, or a material which contains transitionmetal, silicon, and nitrogen, and satisfies the conditions of Formula(1) below:

C_(N)≤9.0×10⁻⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³−7.718×10⁻² ×R _(M)²+3.611×R _(M)−21.084   Formula (1)

wherein R_(M) is a ratio [%] of the content [atom %] of transition metalto the total content [atom %] of transition metal and silicon in saidone layer, and C_(N) [atom %] is the content [atom %] of nitrogen insaid one layer.

While the transition metal includes one or more metals of molybdenum(Mo), tantalum (Ta), tungsten (W), titanium (Ti), chromium (Cr), hafnium(Hf), nickel (Ni), vanadium (V), zirconium (Zr), ruthenium (Ru), rhodium(Rh), niobium (Nb), indium (In), tin (Sn), and palladium (Pd), etc., oralloys of these metals, molybdenum is especially preferable. A materialfor the light-shielding film 4 may contain, in addition to the abovetransition metal and silicon, elements such as nitrogen (N), oxygen (O),carbon (C), hydrogen (H), and boron (B). However, the oxygen contentshould be 5 at % or less, preferably 3 at % or less, and it is furtherpreferable that oxygen is not positively contained (the result of acomposition analysis, such as RBS or XPS, is not more than a detectionlower limit). Further, the material for the light-shielding film 4 maycontain the inert gas such as helium (He), argon (Ar), krypton (Kr), andxenon (Xe).

The light-shielding film 4 is comprised of a single layer structure, ora laminated structure having two or more layers. The single layerstructure allows for the thinnest light-shielding film 4. Thus, ifthinning of the light-shielding film 4 is further pursued, it ispreferable that the light-shielding film 4 is configured to have thesingle layer structure, and that the light-shielding film 4 is entirelymade of the material which contains transition metal and silicon, butdoes not contain nitrogen and oxygen, or the material which containstransition metal, silicon, and nitrogen, and satisfies the conditions ofFormula (1) above.

In addition to the condition that the light-shielding film 4 satisfiesthe predetermined optical density with respect to the ArF exposurelight, the condition on a surface reflectance of the light-shieldingfilm with respect to the ArF exposure light (e.g., 40% or less,preferably 30% or less) is often imposed on the light-shielding film 4.In such a case, the light-shielding film preferably includes a structurein which an upper layer and a lower layer are laminated in said orderfrom the side farthest from the transparent substrate. In particular,the lower layer is made of a material with high optical density, thatis, the material which contains transition metal and silicon, but doesnot contain nitrogen and oxygen, or the material which containstransition metal, silicon, and nitrogen, and satisfies the conditions ofFormula (1) above. Further, the upper layer is made of a material withrelatively low optical density so as to have a function for decreasingthe surface reflectance. Also, the light-shielding film 4 may be formedas a compositional gradient film so as to have an inner structurecomprised of a region made of the above described material with highoptical density and a region made of the above described material withrelatively low optical density.

While the upper layer may be made of a material other than thetransition metal silicide-based material, it is preferably made of amaterial which contains transition metal, silicon, and nitrogen. In thiscase, the total content of nitrogen and oxygen in the upper layer isdesirably 30 at % or more. In view of the thinning of the entirelight-shielding film, the total content of nitrogen and oxygen in theupper layer is preferably 60 at % or less. Since the degree of decreasein extinction coefficient in relation to the content in the upper layeris higher for oxygen than nitrogen, and oxygen may further enhance theexposure light permeability in the upper layer, oxygen can furtherdecrease the surface reflectance. The oxygen content in the upper layeris preferably 10 at % or more, and more preferably 15 at % or more. Onthe other hand, the nitrogen content in the layer is desirably 10 at %or more. However, in order to decrease the surface reflectance whileslightly restraining the oxygen content in the upper layer for thethinning of the light-shielding film, the nitrogen content is preferably15 at % or more, and more preferably 20 at % or more.

When the upper layer is made of the transition metal silicide-basedmaterial, the transition metal content in the upper layer is preferablyless than 10 at %. If the transition metal content in the upper layer is10 at % or more, the phase-shift mask manufactured from this mask blankhas low resistance to mask cleaning (alkaline cleaning with an ammoniahydrogen peroxide mixture, etc., or cleaning with warm water), which maylead to the change in optical properties (increase in surfacereflectance) due to the dissolution of the upper layer. This trend isespecially remarkable when molybdenum is used as the transition metalfor the upper layer.

FIG. 2 is a graph for light-shielding films having respectivepredetermined optical density (OD) values per unit film thickness (1 nm)(in a range from 0.060 [OD/nm] to 0.080 [OD/nm] in increments of 0.005),in which, for each thin film containing molybdenum, silicon, andnitrogen, the horizontal axis shows a ratio obtained by dividing thecontent [atom %] of molybdenum by the total content [atom %] ofmolybdenum and silicon (i.e., the ratio of molybdenum content [atom %]represented as a percentage [%], assuming that the total content [atom%] of molybdenum and silicon in the light-shielding film is 100:hereinafter referred to as Mo/(Mo+Si) ratio), while the vertical axisshows the nitrogen content, and approximate curves for respective filmsare drawn.

In FIG. 2, the results of verification of the light fastness to the ArFexcimer laser exposure light in the thin films each having differentMo/(Mo+Si) ratios and nitrogen contents are also plotted using symbols ∘and ×. The ArF light fastness was verified using a test mask prepared byforming a thin film from the transition metal silicide-based material ona transparent substrate and forming a line-and-space pattern with apattern width (line width) of 200 [nm] in the thin film. The ArF excimerlaser as the exposure light was irradiated to pass through the thin filmfrom the transparent substrate side of the test mask. The ArF excimerlaser was irradiated intermittently, which is the condition close to theactual exposure by an exposure apparatus.

The specific conditions of the ArF excimer laser irradiation were asfollows: emission frequency: 500 [Hz]; energy density per pulse: 10[mJ/(cm²·pulse)]; the number of pulses sequentially emitted: 10; timerequired to sequentially emit 10 pulses: 20 [msec]; pulse width: 5[nsec]; idle period after sequential emission (interval period): 500[msec]. Under these irradiation conditions, intermittent irradiation wasperformed for 15 hours. An accumulated exposure amount for the thin filmintermittently irradiated is 10 [kJ/cm²]. During the ArF excimer laserirradiation, the test mask was placed in the atmosphere at a relativehumidity of 35%RH.

Before and after the irradiation under the above conditions, the patternwidth (line width) of the thin film of the test mask was measured tocalculate an amount of change in line width before and after the ArFexcimer laser irradiation. The thin film of the test mask, in which theamount of change in line width was 10 [nm] or more, was regarded ashaving no ArF light fastness, and plotted in FIG. 2 by putting thesymbol “×” at a location corresponding to the Mo/(Mo+Si) ratio andnitrogen content in the thin film. Similarly, the thin film of the testmask, in which the amount of change in line width was less than 10 [nm],was regarded as having ArF light fastness, and plotted in FIG. 2 byputting the symbol “∘” at a location corresponding to the Mo/(Mo+Si)ratio and nitrogen content in the thin film.

As is clear from the plot with ∘ and × in FIG. 2, it was found that athin film made of a molybdenum silicide-based material should containnitrogen in an amount not less than a predetermined value in order tohave the ArF light fastness. It was also found that the lower limit ofnitrogen content in the presence or absence of ArF light fastnesschanges depending on the Mo/(Mo+Si) ratio. Further, while theverification results for the ArF light fastness or a trend of opticaldensity per unit film thickness in FIG. 2 relate to the thin film madeof the molybdenum silicide-based material, it was also found that asimilar trend is observed in transition metal silicide-based materialsother than the molybdenum silicide-based material (even if thehorizontal axis in FIG. 2 shows the M/(M+Si) ratio, nearly similarresults are obtained).

In the graph of FIG. 2, an approximation formula for an approximatecurve based on plots at which the optical density per unit filmthickness is 0.070 [OD/nm] (plots “▴” in FIG. 2) is Formula (1). Thelight-shielding film 4 may be thinned by using a material falling withinthe lower region including the approximate curve of Formula (1) in FIG.2 (the side where the nitrogen content is low). As is clear from the ArFlight fastness plots using ∘ and × in FIG. 2, the lower region includingthe approximate curve of Formula (1) has difficulty in ArF lightfastness. As described above, when it is intended to provide “aphase-shift mask having ArF light fastness (and a mask blank formanufacturing it)”, a material falling within the region would not beconventionally selected.

When further thinning of the light-shielding film 4 is intended, a ratioR_(M) [%] of the content [atom %] of transition metal to the totalcontent [atom %] of transition metal and silicon, and the nitrogencontent C_(N) [atom %] in the light-shielding film 4 preferably fallwithin a lower region including an approximate curve based on plots for0.075 [OD/nm] in FIG. 2 (plots “□” in FIG. 2). The approximate curve inthis case is defined by Formula (2) below:

C _(N)≤9.84×10⁻⁴ ×R _(M) ³−1.232×10⁻¹ ×R _(M) ²+4.393×R _(M)−33.413   Formula (2)

Further, the ratio R_(M) [%] of the content [atom %] of transition metalto the total content [atom %] of transition metal and silicon, and thenitrogen content C_(N) [atom %] in the light-shielding film 4 preferablyfall within a lower region including an approximate curve based on plotsfor 0.080 [OD/nm] in FIG. 2 (plots “A” in FIG. 2). The approximate curvein this case is defined by Formula (3) below:

C _(N)≤1.355×10⁻³ ×R _(M) ³−1.668×10⁻¹ ×R _(M) ²+6.097×R _(M)−58.784   Formula (3)

Since the approximation formulae, Formula (1) to Formula (3), arecalculated based on respective plots in FIG. 2, they fluctuate withcalculation methods. However, a shift in borders defined based on“M/(M+Si) ratio” and “nitrogen content” satisfying the predeterminedoptical density, which is caused due to the fluctuation in approximationformulae, has a low impact on the optical density variation, which isacceptable.

The entire thickness of the light-shielding film 4 is preferably 50 nmor less, and more preferably 45 nm or less. Also, the entire thicknessof the light-shielding film 4 is preferably 20 nm or more, and morepreferably 25 nm or more. If the light-shielding film 4 is configured tohave a structure in which an upper layer and a lower layer are laminatedin said order from the side farthest from the transparent substrate, thethickness of the upper layer is preferably 3 nm or more, and morepreferably 4 nm or more. Also, the thickness of the upper layer ispreferably 10 nm or less, and more preferably 8 nm or less. In order forthe upper layer to have a function for decreasing the reflectance of thelight-shielding film 4 with respect to the ArF exposure light, and inorder to restrain the reflectance variation in a plane, the thickness ofthe upper layer must be 3 nm or more. The excessively thickened upperlayer is not preferable because the entire thickness of thelight-shielding film 4 inevitably becomes thick.

<<Hard Mask Film>>

A material containing chromium is used for the hard mask film 5 so as toensure the etching selectivity in relation to the light-shielding film 4in the dry etching for the patterning to form the transfer pattern inthe light-shielding film 4. The material for the hard mask film 5 maycontain, in addition to the above described elements, one or moreelements selected from nitrogen (N), oxygen (O), carbon (C), hydrogen(H), and boron (B). Further, in order to improve the etching rate in thedry etching with the chlorine-based gas and oxygen gas, and to enhancedurability to the dry etching with the fluorine-based gas, the materialfor the hard mask film 5 may contain one or more elements selected fromindium (In) and tin (Sn). Moreover, the material for the hard mask film5 may contain an inert gas, such as helium (He), argon (Ar), krypton(Kr), and xenon (Xe). Specifically, the material includes, for example,CrN, CrON, CrOC, and CrOCN.

The thickness of the hard mask film 5 is preferably 3 nm or more, andmore preferably 5 nm or more. If the thickness of the hard mask film 5is less than 3 nm, the reduction in film thickness of the hard mask film5 is progressed in a pattern edge direction before completing the dryetching of the light-shielding film 4 using a hard mask film pattern asa mask, and thus, CD accuracy of the pattern transferred to thelight-shielding film 4 relative to a design pattern may be significantlydecreased. Also, the thickness of the hard mask film 5 is preferably 15nm or less, and more preferably 12 nm or less. If the thickness isgreater than 15 nm, the thickness of the resist film required fortransferring the design pattern to the hard mask film 5 is increased,and thus, it becomes difficult to accurately transfer the fine patternto the hard mask film 5.

Both the etching stopper film 3 and hard mask film 5 are made of thematerial containing chromium, and are patterned by the dry etching usinga mixed gas of oxygen and chlorine. As illustrated in steps formanufacturing a phase-shift mask from the mask blank of Embodiment 1below, even after completing the dry etching for forming the transferpattern (phase-shift pattern) in the etching stopper film 3, the hardmask film 5 should remain on the light-shielding film 4. Therefore, whena thickness of the etching stopper film 3 is Ds, an etching rate of theetching stopper film 3 with respect to the mixed gas of oxygen andchlorine is Vs, a thickness of the hard mask film 5 is Dh, and anetching rate of the hard mask film 5 with respect to the mixed gas ofoxygen and chlorine is Vh, the relationship: (Dh/Vh)>(Ds/Vs) isdesirably satisfied.

After patterning the etching stopper film 3, the hard mask film 5 havingthe thickness of 2 nm or more is preferably left, such that the hardmask film 5 surely remains regardless of the etching conditions untilthe dry etching of the phase-shift film 2 with the fluorine-based gas iscompleted. From this viewpoint, the relationship: Dh−2·Ds·(Vh/Vs)≥2 [nm]is desirably satisfied as well.

In order to configure the etching stopper film 3 and hard mask film 5 tosatisfy the above described conditions, the best way for preparation isto make the etching stopper film 3 and hard mask film 5 from materialshaving substantially the same composition so that the hard mask film 5is thicker than the etching stopper film 3 (preferably, by 2 nm ormore). Another method is to select the material for forming the hardmask film 5 which has a lower etching rate with respect to the mixed gasof oxygen and chlorine than the material for forming the etching stopperfilm 3. In order to increase the etching rate of the chromium-basedmaterial film with respect to the mixed gas of oxygen and chlorine, theincrease in content of oxygen or nitrogen in the material is effective.However, this preparation method has an aspect for decreasing theetching durability to the fluorine-based gas.

If the content of indium (In) or tin (Sn) in the chromium-based materialfilm is increased, the etching rate of the chromium-based material filmwith respect to the mixed gas of chlorine may be increased, though thisis not so remarkable as the increase in etching rate due to the increasein content of oxygen or nitrogen. Furthermore, there is an advantagethat the etching durability with respect to the fluorine-based gas isonly slightly decreased due to the increase in content of indium (In) ortin (Sn) in the chromium-based material film.

Respective layers in the mask blank 10 of Embodiment 1 are describedabove. In the laminated structure, which is comprised of the phase-shiftfilm 2, etching stopper film 3, and light-shielding film 4, in the maskblank according to the present invention, optical density (OD) withrespect to the ArF excimer laser light (wavelength: 193 nm) should be2.7 or more, and is preferably 3.0 or more. In view of functionsrequired of respective films in the above laminated structure (laminatedfilm), the light-shielding film 4 desirably has higher optical density.In accordance with the present embodiment, since the material havinghigh optical density per unit film thickness is used as described above,the film thickness may be thinned. In considering the phase-shift mask,the etching stopper film 3 may be functionally regarded as a part of thelight-shielding film 4 (the light-shielding film is recognized as havinga laminated structure comprised of a plurality of layers), as is clearfrom the above.

Even if the phase-shift film 2 of the present embodiment is configuredto have an optical property of transmittance (10% or more) suitable forthe bright field phase-shift mask, the optical density with respect tothe exposure light should still be 2.7 or more, and is preferably 3.0 ormore, in the laminated structure of the phase-shift film 2, etchingstopper film 3, and light-shielding film 4. In this case, since higheroptical density is required of the light-shielding film 4, the effectobtained by applying the configuration of the light-shielding film 4 ofthe present embodiment becomes greater.

Next, the method for manufacturing a phase-shift mask using the maskblank 10 of the present embodiment described above is explained. FIGS.3(a) to 3(h) are cross-sectional views showing a manufacturing processof a phase-shift mask according to Embodiment 1 of the presentinvention. The method for manufacturing the phase-shift mask accordingto Embodiment 1 is described in accordance with the manufacturingprocess shown in FIGS. 3(a) to 3(h). The configuration of the mask blank10 (FIG. 3(a)) used here is as stated above.

First, a first resist film 6 made of an organic material is formed onthe hard mask film 5 of the mask blank 10 (FIG. 1). Next, a desiredpattern (transfer pattern) to be formed in the phase-shift film 2 isdrawn with an electron beam on the first resist film 6 formed on themask blank 10. After the electron beam drawing, a development process isconducted, thereby forming a first resist pattern 6 a having the desiredtransfer pattern (FIG. 3(a)). Then, the dry etching with the mixed gasof the chlorine-based gas and oxygen gas using the first resist pattern6 a having the transfer pattern as a mask is performed to form a hardmask film pattern 5 a having the transfer pattern (FIG. 3(b)). Thechlorine-based gas used for the mixed gas of the chlorine-based gas andoxygen gas may include, for example, Cl₂, SiCl₄, CHCl₃, CH₂Cl₂, CCl₄,and BCl₃, etc. After forming the hard mask film pattern 5 a, theremaining first resist pattern 6 a is removed.

Next, the dry etching with the fluorine-based gas using the hard maskfilm pattern 5 a as a mask is performed to form a light-shielding filmpattern 4 a having the transfer pattern (FIG. 3(c)). The fluorine-basedgas used here may include SF₆, CHF₃ , CF₄ , C₂ F₆, C₄ F₈, etc.

Then, the dry etching with the mixed gas of the chlorine-based gas andoxygen gas using the light-shielding film pattern 4 a as a mask isperformed to form an etching stopper film pattern 3 a having thetransfer pattern (FIG. 3(d)). Since the hard mask film pattern 5 a isalso etched during the etching for forming the etching stopper filmpattern 3 a, the hard mask film 5 should have been configured to preventthe hard mask film pattern 5 a from disappearing at this stage.

Subsequently, a second resist film 7 is formed on the hard mask filmpattern 5 a, and a desired light-shielding pattern including alight-shielding band to be formed in the light-shielding film 4 is drawnwith an electron beam on the second resist film 7. After the electronbeam drawing, a development process is conducted, thereby forming asecond resist pattern 7 b having the light-shielding pattern. Then, thedry etching with the mixed gas of the chlorine-based gas and oxygen gasusing the second resist pattern 7 b having the light-shielding patternas a mask is performed to form a hard mask film pattern 5 b having thelight-shielding pattern (FIG. 3(e)).

Then, the remaining second resist pattern 7 b is removed, and the dryetching with the fluorine-based gas using as a mask the hard mask filmpattern 5 b having the light-shielding pattern and the etching stopperfilm pattern 3 a having the transfer pattern is performed, such that alight-shielding film pattern 4 b having the light-shielding pattern anda phase-shift film pattern 2 a having the transfer pattern are formed inone step (FIG. 3(f)).

Subsequently, the dry etching with the mixed gas of the chlorine-basedgas and oxygen gas using the light-shielding film pattern 4 b as a maskis performed to form an etching stopper film pattern 3 b having thelight-shielding pattern and to remove the hard mask film pattern 5 b (inone step, (FIG. 3(g))). After that, the predetermined cleaning isconducted, such that a phase-shift mask 20 is obtained (FIG. 3(h)).

The phase-shift mask comprises an alignment mark, which is formed in aperiphery region outside the area in which the transfer pattern isformed, and which is used in alignment upon setting the phase-shift filmon the exposure apparatus (FIG. 3(h)). This alignment mark desirably hasa high contrast, and an alignment mark pattern should have been formedalso in the phase-shift film 2 (that is, a laminated structure portionof the phase-shift film 2, etching stopper film 3, and light-shieldingfilm 4, and a portion where a surface of the substrate 1 is exposedconstitute the alignment mark). In order to form such an alignment mark,the hard mask film 5 should remain upon completing the dry etching withthe mixed gas of the chlorine-based gas and oxygen gas for forming thefine pattern in the etching stopper film 3 (FIG. 3(d)). However, as thethickness of the hard mask film 5 is increased, the thickness of theresist film 6 should also be increased, and thus, the increase inthickness of the hard mask film 5 without limitation is not acceptable.If the light-shielding film 4 having the predetermined optical densitycan be formed to have a thinner thickness, the reduction amount ofthickness of the hard mask film 5 may be reduced upon dry etching thelight-shielding film 4 with the fluorine-based gas. Also, from such aviewpoint, the thinned thickness of the light-shielding film is a veryimportant factor, and according to the present invention, the mask blankin conformity with such requirements may be provided.

In the manufacturing process in FIGS. 3(a) to 3(h), the remaining firstresist pattern 6 a is removed after forming the hard mask film pattern 5a. However, the remaining first resist pattern 6 a may be left as it is.In such a case, the first resist pattern 6 a is left until the processfor forming the light-shielding film pattern 4 a and etching stopperfilm pattern 3 a. The first resist pattern 6 a only has to be left onthe hard mask film pattern 5 a at least until the middle of the dryetching for forming the etching stopper film pattern 3 a. In performingsuch a process, the hard mask film pattern 5 a is protected by the firstresist pattern 6 a at least until the middle of the dry etching forforming the etching stopper film pattern 3 a, and while it is protected,it is not etched with the etching gas comprised of the chlorine-basedgas and oxygen gas. Thus, in this case, the hard mask film 5 and etchingstopper film 3 do not have to satisfy the relationship: (Dh/Vh)>(Ds/Vs).

<Method for Manufacturing a Semiconductor Device>

The phase-shift mask of the present embodiment described above is usedto form a pattern on a semiconductor substrate based on the transferpattern of the phase-shift mask by lithography technology, and thenvarious other steps are performed, such that it is possible tomanufacture a semiconductor device comprising various patterns, etc.formed on the semiconductor substrate.

The exposure apparatus comprises an exposure light source for the ArFexcimer laser exposure light, a projection optical system, a mask stageon which a transfer mask (phase-shift mask) is placed, a stage on whicha semiconductor substrate is placed, etc. The exposure apparatusequipped with a phase-shift mask 20 of the present embodiment andcomprising the semiconductor substrate having a resist film installed onthe stage causes the exposure light obtained from the exposure lightsource for the ArF excimer laser exposure light to be appropriatelyincident on the phase-shift mask 20 through the optical system, suchthat the light transmitted through the phase-shift mask 20 (transferpattern) causes the transfer onto the semiconductor substrate having aresist film through the projection optical system (the transfer patternis transferred to the resist film formed on a transfer targetsubstrate). By performing the etching, etc. using this resist pattern asa mask, for example, a predetermined wiring pattern may be formed on thesemiconductor substrate. The semiconductor device is manufacturedthrough these steps and the other necessary steps. The phase-shift mask20 of the present embodiment is configured in view of the ArF lightfastness, and thus, even if the phase-shift mask 20 is used for a longperiod of time (even if it is irradiated with the ArF excimer laserexposure light for a long period of time), the amount of pattern linewidth variation is restrained within an acceptable range.

Embodiment 2

The mask blank of Embodiment 2 according to the present invention isdescribed below. The mask blank of Embodiment 2 has a configurationsimilar to the mask blank 10 of Embodiment 1 except that theconfiguration of the phase-shift film is different from the mask blank10 of Embodiment 1. The components similar to Embodiment 1 are given thesame reference numerals as Embodiment 1, and their explanations may beeither omitted or simplified. Therefore, the phase-shift film of themask blank of Embodiment 2 is mainly described below.

<<Phase-Shift Film>>

The phase-shift film 2 of Embodiment 2 is comprised of a surface layerand layers other than the surface layer.

The layers other than the surface layer in the phase-shift film 2 aremade by a material, in which transition metal, silicon, and nitrogen arecontained; a M/(M+Si) ratio, that is a ratio of the content [atom %] oftransition metal to the total content [atom %] of transition metal (M)and silicon (Si), is below 9 [%]; and incomplete nitride is contained asa main component. In this case, the transition metal includes one ormore metals of molybdenum (Mo), tantalum (Ta), tungsten (W), titanium(Ti), chromium (Cr), hafnium (Hf), nickel (Ni), vanadium (V), zirconium(Zr), ruthenium (Ru), rhodium (Rh), niobium (Nb), indium (In), tin (Sn),palladium (Pd), etc., or alloys of these metals. In addition to theabove elements, the material of the phase-shift film 2 may containelements such as nitrogen (N), oxygen (O), carbon (C), hydrogen (H), andboron (B). Further, the material of the phase-shift film 2 may containan inert gas, such as helium (He), argon (Ar), krypton (Kr), and xenon(Xe).

In the present invention, incomplete nitride is a compound which has lownitrogen content with respect to the stoichiometric compositionaccording to the valence that a transition metal element or siliconelement can have. That is, it has a few M—N bonds and Si—N bonds. In thepresent invention, the incomplete nitride may be defined as a compoundwhich has fewer M—N bonds and Si—N bonds than the complete nitride.

For example, when a light semitransmissive film containing transitionmetal, silicon, and nitrogen as main components is formed on thetransparent substrate by the sputtering in an atmosphere containingnitrogen, as a flow rate of the nitrogen gas increases, the nitrogencontent in the film also increases (the transmittance increases), but anamount of increase in transmittance relative to the amount of increasein flow rate of the nitrogen gas gradually decreases, which leads to thestate in which the nitrogen content in the film does not increase (thetransmittance does not increase) even if the flow rate of the nitrogengas is increased. In the present invention, this state is referred to ascomplete nitride. Also, the state before the complete nitride state,that is, the state as above in which the nitrogen content in the filmmay increase (the transmittance may increase) if the flow rate of thenitrogen gas is increased, is referred to as incomplete nitride. Theincomplete nitride is included in the state as above in which theincrease in transmittance relative to the increase in flow rate of thenitrogen gas is gradually diminished. The incomplete nitride does notinclude a state that comes before the above described state in which theincrease in transmittance relative to the increase in flow rate of thenitrogen gas is gradually diminished.

For example, when the transition metal is molybdenum, bonding states inrelation to the flow rate of the nitrogen gas are as follows. That is,if the nitrogen flow rate is zero (0 sccm) (in the case of MoSi film),the main bonding states in the film are Si—Si bonds and Mo—Si bonds.Since many Si—Si bonds are included, it is believed that Si oxidationwill affect the light fastness. If the nitrogen flow rate is less than35 sccm (a ratio of the N₂ flow rate to the total flow rate of Ar and N₂[N₂/(Ar+N₂)] is less than 77%) for less nitriding, main bonding statesin the film are Si—Si bonds, Si—N bonds, and Mo—Si bonds. Since manySi—Si bonds are included, it is believed that Si oxidation will affectthe light fastness.

If the nitrogen flow rate is not less than 35 sccm and not more than 50sccm ([N₂/(Ar+N₂)] is not less than 77% and not more than 83%), mainbonding states in the film are Si—N bonds and Mo—Si bonds. Since thereare few Si—Si bonds and Mo—N bonds, Si and Mo are hardly oxidized.Specifically, since the film includes a relatively larger number ofMo—Si bonds than Mo—N bonds, and the number of Mo—N bonds is relativelysmall compared to the situation where the film includes a relativelylarger number of Mo—N bonds than Mo—Si bonds, it is believed that theeffect by Mo oxidation (i.e., decrease in light fastness) will be small.

In the case of a complete nitride film with the nitrogen flow rate beinggreater than 50 sccm ([N₂/(Ar+N₂)] being greater than 83%), the mainbonding states in the film are Si—N bonds and Mo—N bonds. Since Mo—Nbonds are included, Mo is oxidized. Specifically, since the filmincludes a relatively larger number of Mo—N bonds than Mo—Si bonds, andthe number of Mo—N bonds is relatively large compared to the situationwhere the film includes a relatively larger number of Mo—Si bonds thanMo—N bonds, it is believed that the effect by Mo oxidation (i.e.,decrease in light fastness) will be large.

If the M/(M+Si) ratio in the layers other than the surface layer in thephase-shift film 2 is less than 9%, the above described effects areobtained. On the other hand, as the M/(M+Si) ratio becomes high, theabove described effects may not be exhibited. Further, from theviewpoint that the Mo content in the film is further reduced and Mo—Nbonds are further decreased (the light fastness is further improved),the M/(M+Si) ratio is preferably less than 7%, or less than 5%.

The transmittance of the phase-shift film 2 at a wavelength of the abovedescribed exposure light is preferably not less than 4% and below 9%. Ifthe transmittance is greater than 9%, it is difficult to achieve theincomplete nitride state, and thus, it is also difficult to obtain theabove described effects. In particular, the transmittance greater than9% leads to the complete nitride state even if the nitrogen gas flowrate is reduced to about zero (therefore, the incomplete nitride statecannot be achieved). The more preferable range for transmittance is 8%or less. If the transmittance is less than 4%, the film thickness isincreased. The transmittance here refers to the transmittance after filmformation without annealing, etc. Therefore, when annealing for stressreduction, etc., the film must be formed in expectation of variation intransmittance due to the annealing. The phase-shift film 2 is preferablyprepared such that the phase difference between the ArF exposure lighttransmitted therethrough and the light traveling through air for thesame distance as the thickness of the phase-shift film 2 is within arange of 150 to 180 degrees.

The incomplete nitride film includes Mo—N bonds and Mo—Si bonds, andpreferably includes a relatively larger number of Mo—Si bonds than Mo—Nbonds. It is preferable because the film includes, as bonding states, arelatively larger number of Mo—Si bonds than Mo—N bonds, and thus Si andMo are less oxidized, and the light fastness becomes high. Further, theincomplete nitride film preferably mainly includes Si—N bonds and Mo—Sibonds. It is preferable because when the main bonding states in the filmare Si—N bonds and Mo—Si bonds, there is almost no Si—Si bond and Mo—Nbond, and thus, Si and Mo are less oxidized, and the light fastnessbecomes high. The main bonding state in the film relates to portionsother than the surface layer portion where an oxidized layer, etc. isformed by annealing, etc.

The nitrogen content in the layers other than the surface layer in thephase-shift film 2 is preferably not less than 40 at % and not more than47 at %. While there may be an effect from the Mo content ortransmittance in the film, it becomes difficult to achieve theincomplete nitride state if the nitrogen content in the phase-shift film2 is greater than 47 at %. If the nitrogen content in the phase-shiftfilm 2 is less than 40 at %, Si—Si bonds increase, such that the lightfastness tends to be deteriorated. Further, the nitrogen content in thelayers other than the surface layer in the phase-shift film 2 ispreferably less than the nitrogen content in the complete nitride filmby not less than 2 at % and not more than 20 at %. If the nitrogencontent in the layers other than the surface layer in the phase-shiftfilm 2 is lower than the nitrogen content in the complete nitride byless than 2 at %, it becomes difficult to achieve the incomplete nitridestate. If the nitrogen content in the layers other than the surfacelayer in the phase-shift film 2 is lower than the nitrogen content inthe complete nitride by more than 20 at %, Si—S bonds increase, and thelight fastness tends to be deteriorated.

The steps for manufacturing a phase-shift mask from the mask blank 10 ofthe present embodiment and the method for manufacturing a semiconductordevice using the phase-shift mask are similar to those of Embodiment 1,and thus, their explanations are omitted here.

Embodiment 3

The mask blank of Embodiment 3 according to the present invention isdescribed now. The mask blank of Embodiment 3 has a configurationsimilar to the mask blank 10 of Embodiment 1 except that theconfiguration of the phase-shift film is different from the mask blank10 of Embodiment 1. The components similar to Embodiment 1 are given thesame reference numerals as Embodiment 1, and their explanations may beeither omitted or simplified. Therefore, the phase-shift film of themask blank of Embodiment 3 is mainly described below.

<<Phase-Shift Film>>

The phase-shift film 2 of Embodiment 3 is comprised of a surface layerand layers other than the surface layer, and characterized in that thelayers other than the surface layer are made of a material consisting ofsilicon and nitrogen, or a material consisting of silicon, nitrogen, andone or more elements selected from metalloid elements, non-metallicelements, and noble gases (these materials are referred to assilicon-based materials below). As mentioned above, the ArF exposurelight irradiation causes an altered layer to be formed on a surfacelayer of the phase-shift film pattern made of the transition metalsilicide-based material. A factor promoting growth of the altered layeris the presence of transition metal. In the phase-shift film ofEmbodiment 3, since a silicon-based material which does not contain sucha factor, transition metal, is applied, the ArF light fastness isenhanced. The phase-shift film except for the inevitably oxidizedsurface layer (oxidized layer) may be a single layer structure or alaminated structure comprised of a plurality of layers.

It is possible to form, from a single layer film (including the oxidizedlayer as the surface layer) made of the silicon-based material, aphase-shift film with optical properties so as to allow for thetransmission at a predetermined transmittance and a predetermined phasedifference with respect to the ArF exposure light. However, if thephase-shift film is made of a material having such optical properties bythe sputtering method, some methods used may result in the filmformation conditions under which it is difficult to stably form a filmwith high uniformity in optical properties or a film with a low defectrate. The phase-shift film 22 having a laminated structure shown in FIG.4 may solve the problem of the film-forming stability. FIG. 4 is across-sectional view showing a layered configuration of a mask blank 102according to a variant of Embodiment 3. As shown in FIG. 4, thephase-shift film 22 in this variant comprises a low-transmittance layer221, a high-transmittance layer 222, and an uppermost layer 223.

The inventors did an earnest study on a measure for forming a film whichhas high uniformity in optical properties or composition in a filmthickness direction and a low defect rate when the phase-shift film iscomprised of a silicon-based material film containing silicon andnitrogen but no transition metal. In order to form on a substrate thesilicon-based material film containing silicon and nitrogen but notransition metal by the current film forming technique so as to havehigh uniformity in optical properties or composition, the technique forfilm formation by reactive sputtering must be applied. However,formation of thin film by reactive sputtering may often cause aphenomenon in which a film forming rate or voltage for the thin filmvary depending on a mixing ratio of the reactive gas in a film formingchamber.

FIG. 5 is a graph schematically showing a general trend of change indeposition rate, which is found when a thin film is formed by thereactive sputtering and a mixing ratio of a reactive gas in a mixed gasof a noble gas and the reactive gas in a film forming chamber (or a flowratio of the reactive gas in the mixed gas) is changed. FIG. 5 shows acurve I which shows a change in deposition rate when the mixing ratio ofthe reactive gas in the mixed gas is gradually increased (increasemode), and a curve D which shows a change in deposition rate when themixing ratio of the reactive gas in the mixed gas is gradually decreased(decrease mode). Generally, in an area where the mixing ratio of thereactive gas in the mixed gas is low (area of metal mode M in FIG. 5)and an area where the mixing ratio of the reactive gas in the mixed gasis high (area of reactive mode R in FIG. 5), both the increase anddecrease modes have a small fluctuation range for the deposition rateassociated with the change in mixing ratio of the reactive gas in themixed gas. Also, the difference in deposition rate between the increaseand decrease modes is small at the same mixing ratio of the reactive gasin the mixed gas. Thus, the thin film may be stably formed in the areasof metal mode M and reactive mode R. That is, the areas of metal mode Mand reactive mode R enable formation of thin film having high uniformityin composition and optical properties and a low defect rate.

On the other hand, in an area of transition mode T between the areas ofmetal mode M and reactive mode R in FIG. 5, a fluctuation range for thedeposition rate associated with the change in mixing ratio of thereactive gas in the mixed gas is large, both in the increase anddecrease modes. Also, the difference in deposition rate between theincrease and decrease modes is large at the same mixing ratio of thereactive gas in the mixed gas. In the area of transition mode T, thedeposition rate greatly fluctuates due to a slight change in mixingratio of the reactive gas in the mixed gas in the film forming chamber,and the slight change in mixing ratio causes the fluctuation indeposition rate due to a shift from the increase mode to decrease mode.Therefore, the thin film is formed while the deposition rate isunstable. The fluctuation in deposition rate affects an amount ofcomponent of the reactive gas contained in the thin film. That is, inthe area of transition mode T, it is difficult to form a thin film whichhas high uniformity in composition and optical properties and a lowdefect rate.

If a phase-shift film having a single layer structure which is comprisedof the silicon-based material film containing no transition metal isformed by the reactive sputtering, it is highly necessary to form thefilm in the area of transition mode T in view of restrictions onrequired optical properties. There is a method to find a combinedreactive gas which provides a small difference in deposition ratebetween the increase and decrease modes in the transition mode T at thesame mixing ratio of the reactive gas in the mixed gas. However, even ifsuch a combined reactive gas is found, there is still a problem of largefluctuation range in the deposition rate associated with the change inmixing ratio of the reactive gas in the mixed gas within the area oftransition mode T.

If the silicon-based material film containing silicon and nitrogen butno transition metal is formed by the reactive sputtering in the area ofmetal mode, so as to try to ensure the film thickness for obtaining aphase difference required of a phase-shift film, an extinctioncoefficient k for the material of the formed film is high, and thus, thetransmittance to ArF exposure light is lower than the requiredtransmittance. Such a film is difficult to cause a phase-shift effect,and thus, it is not suitable for the phase-shift film. On the otherhand, if the silicon-based material film containing silicon and nitrogenbut no transition metal is formed by the reactive sputtering in the areaof reactive mode, so as to try to ensure the film thickness forobtaining a phase difference required of a phase-shift film, anextinction coefficient k for the material of the formed film is low, andthus, the transmittance to ArF exposure light is higher than therequired transmittance. With such a film, the phase-shift effect can beobtained, but the resist film on the semiconductor wafer may be exposedto the light transmitted from a pattern portion other than the areawhere the phase-shift effect is caused, and thus, it is also notsuitable for the phase-shift film.

After the earnest study on a means for solving many technical problemswhich arise in achievement of the phase-shift film suitable for the ArFexposure light by the silicon-based material film containing silicon andnitrogen but no transition metal, the inventors reached the conclusionthat the above technical problems can be solved by the phase-shift filmhaving a laminated structure of a low-transmittance layer that is asilicon-based material film formed by reactive sputtering in the area ofmetal mode and a high-transmittance layer that is a silicon-basedmaterial film formed by reactive sputtering in the area of reactivemode.

That is, as shown in FIG. 4, the phase-shift film 22 of the presentembodiment includes a structure in which a low-transmittance layer 221and a high-transmittance layer 222 are laminated; the low-transmittancelayer 221 and high-transmittance layer 222 are made of a materialconsisting of silicon and nitrogen, or a material consisting of silicon,nitrogen, and one or more elements selected from metalloid elements,non-metallic elements, and noble gases; and the low-transmittance layer221 is formed to have a relatively lower nitrogen content than thehigh-transmittance layer 222.

The low-transmittance layer 221 and high-transmittance layer 222 in thephase-shift film 22 of the present embodiment are formed by alow-transmittance layer forming step and a high-transmittance layerforming step, respectively. In the low-transmittance layer forming step,a silicon target, or a target made of a material consisting of siliconand one or more elements selected from metalloid elements andnon-metallic elements is used to perform the reactive sputtering in asputtering gas comprising the nitrogen-based gas and noble gas so as toform the low-transmittance layer 221 on the transparent substrate 1. Inthe high-transmittance layer forming step, a silicon target, or a targetmade of a material consisting of, in addition to silicon, one or moreelements selected from metalloid elements and non-metallic elements isused to perform the reactive sputtering in a sputtering gas comprisingthe nitrogen-based gas and noble gas and having a higher mixing ratio ofthe nitrogen-based gas than the step for forming the low-transmittancelayer 221, so as to form the high-transmittance layer 222.

The sputtering gas used in the low-transmittance layer forming step isselected such that the mixing ratio of the nitrogen-based gas is lowerthan a mixing ratio range which causes the transition mode with atendency of unstable film formation. The sputtering gas used in thehigh-transmittance layer forming step is selected such that the mixingratio of the nitrogen gas is higher than the mixing ratio range whichcauses the transition mode.

In the present embodiment, the phase-shift film 22 is not a single layerstructure, but a laminated structure of the low-transmittance layer 221and high-transmittance layer 222. By forming such a laminated structure,the low-transmittance layer 221 may be formed by the reactive sputteringin the area of metal mode in which a film having low nitrogen contenttends to be formed; and the high-transmittance layer 222 may be formedby the reactive sputtering in the area of reactive mode in which a filmhaving high nitrogen content tends to be formed. Thus, both thelow-transmittance layer 221 and high-transmittance layer 222 may beformed by the reactive sputtering under the film forming conditionswhich have small variation in film forming rate or voltage upon the filmformation. As a result, it is possible to form the phase-shift filmhaving high uniformity in composition and optical properties and a lowdefect rate.

The low-transmittance layer 221 and high-transmittance layer 222 aremade of a material consisting of silicon and nitrogen, or a materialconsisting of silicon, nitrogen, and one or more elements selected frommetalloid elements, non-metallic elements, and noble gases. Thelow-transmittance layer 221 and high-transmittance layer 222 do notcontain transition metal, which can be a factor for lowering the lightfastness to the ArF exposure light (that is, the phase-shift film 22 ofthe present embodiment has the ArF light fastness). Further, thelow-transmittance layer 221 and high-transmittance layer 222 desirablydo not contain metallic elements other than transition metal, since itis undeniable that they may become a factor for lowering the lightfastness to ArF exposure light. The low-transmittance layer 221 andhigh-transmittance layer 222 may contain any of metalloid elements, inaddition to silicon. They preferably contain one or more elementsselected from boron, germanium, antimony, and tellurium among themetalloid elements, since the increase in conductivity of silicon usedas a sputtering target may be expected.

The low-transmittance layer 221 and high-transmittance layer 222 maycontain any of non-metallic elements, in addition to nitrogen. Theypreferably contain one or more elements selected from carbon, fluorine,and hydrogen among the non-metallic elements. The low-transmittancelayer 221 and high-transmittance layer 222 preferably have oxygencontent of 10 at % or less, and more preferably 5 at % or less. Furtherpreferably, they do not positively contain oxygen (the result of thecomposition analysis, such as RBS or XPS, is not more than the detectionlower limit). If the silicon-based material film contains oxygen, theextinction coefficient k tends to significantly decrease, whichincreases the entire thickness of the phase-shift film. The transparentsubstrate is generally made of a material containing SiO₂ such assynthetic quartz glass as a main component. If one of thelow-transmittance layer 221 and high-transmittance layer 222 is formedin contact with a surface of the transparent substrate, and thesilicon-based material film contains oxygen, the difference incomposition between the silicon-based material film containing oxygenand the glass is small, which may cause the problem that the etchingselectivity between the silicon-based material film and transparentsubstrate 1 is difficult to obtain in the dry etching for forming apattern in the phase-shift film 22.

A target made of a material which consisting of silicon and one or moreelements selected from metalloid elements and non-metallic elementspreferably contains one or more elements selected from boron, germanium,antimony, and tellurium as metalloid elements. Since these metalloidelements are expected to enhance conductivity of the target, the targetdesirably contains these metalloid elements especially when thelow-transmittance layer 221 and high-transmittance layer 222 are formedby the DC sputtering method.

The low-transmittance layer 221 and high-transmittance layer 222 maycontain a noble gas. The noble gas is an element which exists in thefilm forming chamber during forming the thin film by reactivesputtering, thereby increasing the deposition rate and improvingproductivity. The noble gas is turned into plasma and collides with thetarget, and thus, the target constituent element jumps out of thetarget, and is laminated onto the transparent substrate 1 whileincorporating the reactive gas, such that the thin film is formed.Between the jumping of the target constituent element out of the targetand its adhesion to the transparent substrate 1, the noble gas withinthe film forming chamber is slightly incorporated. The preferable noblegas required in the reactive sputtering includes argon, krypton, andxenon. Further, in order to relieve the stress in the thin film, heliumor neon with a small atomic weight may be positively incorporated in thethin film.

In the low-transmittance layer forming step for forming thelow-transmittance layer 221 and the high-transmittance layer formingstep for forming the high-transmittance layer 222 for the phase-shiftfilm 22, the nitrogen-based gas is contained in the sputtering gas. Anygases containing nitrogen may be applicable as the nitrogen-based gas.As stated above, since the low-transmittance layer 221 andhigh-transmittance layer 222 preferably have low oxygen content, thenitrogen-based gas containing no oxygen is preferably applied, and thenitrogen gas (N₂ gas) is more preferably applied.

The low-transmittance layer 221 and high-transmittance layer 222 in thephase-shift film 22 are preferably laminated in direct contact with eachother without any film therebetween. Further, in the film structure, itis preferable that the film made of a material containing a metallicelement does not contact either the low-transmittance layer 221 or thehigh-transmittance layer 222. It is because if the heat treatment orirradiation of ArF exposure light is performed while the film containingsilicon is in contact with the film containing a metallic element, themetallic element tends to easily diffuse into the film containingsilicon.

The low-transmittance layer 221 and high-transmittance layer 222 arepreferably comprised of the same constituent element. If one of thelow-transmittance layer 221 and high-transmittance layer contains adifferent constituent element, and the heat treatment or irradiation ofArF exposure light is performed while these layers are laminated incontact with each other, the different constituent element may move toand diffuse into the layer not containing that constituent element.Also, the optical properties of the low-transmittance layer 221 andhigh-transmittance layer 222 may significantly change compared to theoptical properties at the time of formation of the layers. Inparticular, when the different constituent element is a metalloidelement, the low-transmittance layer 221 and high-transmittance layer222 must be formed using different respective targets.

The low-transmittance layer 221 and high-transmittance layer 222 may belaminated in the phase-shift film 22 in any order from the transparentsubstrate side. If the low-transmittance layer 221 andhigh-transmittance layer 222 are laminated in said order from the sideof and adjacent to the transparent substrate 1, the low-transmittancelayer 221 is a silicon-containing film with low nitrogen content, suchthat the etching selectivity may be easily achieved in relation to thetransparent substrate 1 made of a material containing SiO₂ as a maincomponent. While the etching gas used in the dry etching for forming apattern in the silicon-containing film is generally the fluorine-basedgas, a chlorine-based gas is also applicable as an etching gas in thesilicon-containing film with low nitrogen content. By using thechlorine-based gas in the dry etching of the low-transmittance layer221, the etching selectivity in relation to the transparent substrate 1may be significantly enhanced.

If the high-transmittance layer 222 and low-transmittance layer 221 arelaminated in said order from the side of and adjacent to the transparentsubstrate 1, the high-transmittance layer 222 is a silicon-containingfilm with high nitrogen content. Thus, if the high-transmittance layer222 is formed in contact with the transparent substrate 1 made of amaterial containing SiO₂ as a main component, the high adherence may beeasily obtained between the surface of the transparent substrate 1 andthe high-transmittance layer 222.

The low-transmittance layer 221 and high-transmittance layer 222 in thephase-shift film 22 are preferably laminated in contact with each otherwithout any other film therebetween, since the silicon-containing filmpreferably does not contact the film made of a material containing ametallic element for the above reason.

When one low-transmittance layer 221 and one high-transmittance layer222 are considered as one laminated structure, the phase-shift film 22preferably has two or more laminated structures. One of thelow-transmittance layer 221 and high-transmittance layer 222 preferablyhas a thickness of 20 nm or less. Since the low-transmittance layer 221and high-transmittance layer 222 are significantly different in requiredoptical properties, there is a large difference in nitrogen content inthe film therebetween. Therefore, there is a great difference in etchingrate in the dry etching with the fluorine-based gas between thelow-transmittance layer 221 and high-transmittance layer 222. If thephase-shift film is comprised of one low-transmittance layer 221 and onehigh-transmittance layer 222, i.e., a two-layer structure, when thepattern is formed by the dry etching with the fluorine-based gas, a stepis easily generated in a pattern cross-section of the phase-shift filmafter the etching. Assuming that one low-transmittance layer 221 and onehigh-transmittance layer 222 are considered as one laminated structure,when the phase-shift film is configured to have two or more laminatedstructures, the thickness of each (one layer) of the low-transmittancelayer 221 and high-transmittance layer 222 is thinner than the abovedescribed two-layer structure (one laminated structure), and thus, it ispossible to reduce the step generated in the pattern cross-section ofthe phase-shift film after the etching. The thickness of each (onelayer) of the low-transmittance layer 221 and high-transmittance layer222 is limited to 20 nm or less, thereby further controlling the stepgenerated in the pattern cross-section of the phase-shift film after theetching.

The low-transmittance layer 221 in the phase-shift film 22 of thepresent invention is a silicon-based material film which has lownitrogen content and does not positively contain oxygen. Therefore, ittends to be easily etched with a fluorine-based gas in an unexcitedstate, such as XeF₂, in the correction of EB defect. Thus, thelow-transmittance layer 221 is desirably placed such that it isdifficult to contact the fluorine-based gas in an unexcited state, suchas XeF₂. On the other hand, since the high-transmittance layer 222 is asilicon-based material film with high nitrogen content, it is not easilysubject to the influence of the fluorine-based gas in an unexcitedstate, such as XeF₂. As stated above, when one low-transmittance layer221 and one high-transmittance layer 222 are considered as one laminatedstructure, and the phase-shift film is formed to have two or morelaminated structures, the low-transmittance layer 221 may be configuredto be sandwiched between two high-transmittance layers 222, or betweenthe transparent substrate 1 and high-transmittance layer 222. Therefore,while the fluorine-based gas in an unexcited state, such as XeF₂, mayinitially contact and etch the low-transmittance layer 221, it thenbecomes hard to contact the low-transmittance layer 221 (since a surfaceof a side wall of the low-transmittance layer 221 becomes morecomplicated than a surface of a side wall of the high-transmittancelayer 222, it is hard for the gas to enter the surface of the side wallof the low-transmittance layer 221). Accordingly, with this laminatedstructure, it is possible to control the etching of thelow-transmittance layer 221 with the fluorine-based gas in an unexcitedstate, such as XeF₂. Further, the thickness of each of thelow-transmittance layer 221 and high-transmittance layer 222 is limitedto 20 nm or less, such that it is possible to further control theetching of the low-transmittance layer 221 with the fluorine-based gasin an unexcited state, such as XeF₂.

The low-transmittance layer 221 and high-transmittance layer 222 arepreferably made of a material consisting of silicon and nitrogen. In thelow-transmittance layer forming step of the method for manufacturing themask blank, it is preferable that a silicon target is used to performthe reactive sputtering in the sputtering gas comprising the nitrogengas and noble gas so as to form the low-transmittance layer 221. In thehigh-transmittance layer forming step, it is preferable that a silicontarget is used to perform the reactive sputtering in a sputtering gascomprising the nitrogen gas and noble gas so as to form thehigh-transmittance layer 222.

As stated above, containing the transition metal in thelow-transmittance layer 221 and high-transmittance layer 222 may be afactor for lowering the light fastness to the ArF exposure light. If thelow-transmittance layer 221 and high-transmittance layer 222 contain anymetal other than the transition metal or any metalloid element otherthan silicon, the optical properties may change as the contained metalor metalloid element moves between the low-transmittance layer 221 andhigh-transmittance layer 222. As for the non-metallic element, if thelow-transmittance layer 221 and high-transmittance layer 222 containoxygen, the transmittance to ArF exposure light is significantlyreduced. In view of these aspects, the low-transmittance layer 221 andhigh-transmittance layer 222 are further preferably made of a materialconsisting of silicon and nitrogen. The noble gas is an element which ishardly detected even if a composition analysis, such as RBS or XPS, isconducted on the thin film. Thus, the above material consisting ofsilicon and nitrogen may be regarded as including a material containinga noble gas.

The phase-shift film 22 of the present embodiment comprises, at alocation furthest from the transparent substrate, an uppermost layer 223which is made of a material consisting of silicon, nitrogen, and oxygen,or a material consisting of silicon, nitrogen, oxygen, and one or moreelements selected from metalloid elements, non-metallic elements, andnoble gases. A silicon target, or a target made of a material consistingof silicon and one or more elements selected from metalloid elements andnon-metallic elements is used to perform the sputtering in a sputteringgas comprising a noble gas, so as to form the uppermost layer 223 at thelocation furthest from the transparent substrate in the phase-shift film(uppermost layer forming step). Further, a silicon target may be used toperform the reactive sputtering in the sputtering gas comprising anitrogen gas and a noble gas, so as to form the uppermost layer 223 atthe location furthest from the transparent substrate in the phase-shiftfilm and then perform a treatment for oxidizing at least a surface layerof the uppermost layer 223 (uppermost layer forming step).

The silicon-based material film which does not positively contain oxygenbut contains nitrogen has high light fastness to the ArF exposure light,but has a lower chemical resistance than the silicon-based material filmpositively containing oxygen. If the mask blank comprises thehigh-transmittance layer 222 or low-transmittance layer 221, which doesnot positively contain oxygen but contains nitrogen, placed as anuppermost layer of the phase-shift film opposite from the transparentsubstrate, it is difficult to avoid oxidation of the surface layer ofthe phase-shift film due to mask cleaning or storage in the atmospherefor the phase-shift mask manufactured from the mask blank. If thesurface layer of the phase-shift film is oxidized, the opticalproperties significantly change compared to the optical properties atthe time of formation of the thin film. Especially when thelow-transmittance layer 221 is provided as the uppermost layer of thephase-shift film, a degree of increase in transmittance due to theoxidation of the low-transmittance layer 221 becomes large. Byconfiguring the phase-shift film to further comprise, on the laminatedstructure of the low-transmittance layer 221 and high-transmittancelayer 222, the uppermost layer 223 made of a material consisting ofsilicon, nitrogen, and oxygen, or a material consisting of silicon,nitrogen, oxygen, and one or more elements selected from metalloidelements, non-metallic elements, and noble gases, the surface oxidationof the low-transmittance layer 221 and high-transmittance layer may berestrained.

The uppermost layer 223 made of a material consisting of silicon,nitrogen, and oxygen, or a material consisting of silicon, nitrogen,oxygen, and one or more elements selected from metalloid elements,non-metallic elements, and noble gases may include a configurationhaving substantially the same composition in a thickness direction ofthe layer, as well as a configuration with a compositional gradient inthe thickness direction of the layer (a configuration having acompositional gradient in which the oxygen content in the uppermostlayer 223 increases with distance from the transparent substrate 1).SiO₂ and SiON are suitable for the material for forming the uppermostlayer 223 having substantially the same composition in the thicknessdirection of the layer. In the case of the uppermost layer 223 with acompositional gradient in the thickness direction of the layer, it ispreferable that the transparent substrate 1 side is SiN, the oxygencontent increases with distance from the transparent substrate 1, andthe surface layer is SiO₂ o r SiON.

For the formation of the uppermost layer 223, the uppermost layerforming step may be applied, in which a silicon target, or a target madeof a material consisting of silicon and one or more elements selectedfrom metalloid elements and non-metallic elements is used to perform thereactive sputtering in the sputtering gas containing the nitrogen gas,oxygen gas, and noble gas so as to form the uppermost layer 223. Theuppermost layer forming step may also be applied to the formation of theuppermost layer having substantially the same composition in thethickness direction of the layer, and the uppermost layer 223 with acompositional gradient. Also, for the formation of the uppermost layer223, an uppermost layer forming step may be applied, in which a silicondioxide (SiO₂) target, or a target made of a material containing, inaddition to silicon dioxide (SiO₂), one or more elements selected frommetalloid elements and non-metallic elements is used to perform thesputtering in the sputtering gas containing the noble gas so as to formthe uppermost layer 223. This uppermost layer forming step may also beapplied to the formation of the uppermost layer 223 having substantiallythe same composition in the thickness direction of the layer, and theuppermost layer 223 with a compositional gradient.

For the formation of the uppermost layer 223, an uppermost layer formingstep may be applied, in which a silicon target, or a target made of amaterial containing, in addition to silicon, one or more elementsselected from metalloid elements and non-metallic elements is used toperform the reactive sputtering in the sputtering gas containing thenitrogen gas and noble gas so as to form the uppermost layer 223 andfurther perform a treatment for oxidizing at least a surface layer ofthe uppermost layer 223. This uppermost layer forming step may bebasically applied to the formation of the uppermost layer 223 with acompositional gradient in the thickness direction of the layer. In thiscase, the treatment for oxidizing the surface layer of the uppermostlayer 223 may include a heat treatment in a gas containing oxygen, suchas in the atmosphere, or a treatment for bringing ozone or oxygen plasmainto contact with the uppermost layer 223.

While the low-transmittance layer 221, high-transmittance layer 222, anduppermost layer 223 in the phase-shift film 22 are formed by sputtering,any sputtering, such as DC sputtering, RF sputtering, and ion beamsputtering may be applied. When a target with low conductivity (asilicon target, a silicon compound target which contains no metalloidelement or has a low content of metalloid element, etc.) is used, the RFsputtering or ion beam sputtering is preferably applied. However, RFsputtering is more preferably applied in view of film forming rate.

The transmittance to ArF exposure light of the phase-shift film 22 ofthe present embodiment is preferably 1% or more, and more preferably 2%or more, in order to effectively exhibit the phase-shift effect. Thephase-shift film 22 is prepared such that the transmittance to ArFexposure light is preferably 30% or less, more preferably 20% or less,and further preferably 18% or less. The phase-shift film 22 ispreferably prepared such that the phase difference between the ArFexposure light transmitted therethrough and the light traveling throughair for the same distance as the thickness of the phase-shift film 22 iswithin a range of 150 to 180 degrees.

If NTD (Negative Tone Development) process is used as anexposure/development process for the resist film on the wafer, thebright field mask (transfer mask having a high pattern opening ratio) isused. In the bright field phase-shift mask, when the transmittance ofthe phase-shift film is higher, the balance between 0-order light andfirst order light for the light transmitted through a transparentportion is better, thereby improving a pattern resolution on the resistfilm. It is because there is a greater effect that the exposure lighttransmitted through the phase-shift film interferes with the 0-orderlight to attenuate the light intensity. When the phase-shift film 22 isapplied to the bright field phase-shift mask, the transmittance at anexposure wavelength in the phase-shift film 22 is more preferably 10% ormore. Also in this case, the transmittance at an exposure wavelength inthe phase-shift film 22 is preferably 30% or less, and more preferably20% or less.

If the phase-shift film 22 of the present embodiment is configured tohave an optical property of transmittance (10% or more) suitable for thebright field phase-shift mask, the optical density with respect to theexposure light should still be 2.7 or more, and is preferably 3.0 ormore, in the laminated structure of the phase-shift film 22, etchingstopper film 3, and light-shielding film 4. In this case, since higheroptical density is required of the light-shielding film 4, the effectobtained by applying the configuration of the light-shielding film 4 ofthe present embodiment becomes greater.

The process for manufacturing a phase-shift mask from the mask blank 102of the present embodiment is similar to Embodiment 1 (in that the dryetching with the fluorine-based gas is performed, but the composition ofthe phase-shift film is different), and the method for manufacturing asemiconductor device using the phase-shift mask is also similar toEmbodiment 1. Therefore, their explanations are omitted here.

EXAMPLES

Each embodiment of the present invention is described below in furtherdetail based on examples.

Example 1 [Manufacture of Mask Blank]

A transparent substrate 1 having a main surface dimension of about 152mm×about 152 mm and a thickness of about 6.35 mm and made of syntheticquartz glass was prepared. End faces and the main surface of thetransparent substrate 1 were polished to have predetermined surfaceroughness, and then, the transparent substrate 1 was subjected topredetermined cleaning and drying processes.

Then, the transparent substrate 1 was placed in a single-wafer RFsputtering device, a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=3 at %:97 at %) was used, and reactive sputtering (DC sputtering)in a mixed gas atmosphere of argon (Ar), nitrogen (N₂), and helium (He)was performed, such that the phase-shift film 2 made of molybdenum,silicon, and nitrogen (MoSiN film) and having a film thickness of 63 nmwas formed on the transparent substrate 1.

Then, on the transparent substrate 1 with the phase-shift film 2 formedthereon, a heat treatment was performed so as to reduce film stress ofthe phase-shift film 2 and to form an oxidized layer on a surface layer.In particular, a heating furnace (electric furnace) was used to conductthe heat treatment at a heating temperature of 450° C. in the air forone hour. The phase-shift film 2 after the heat treatment was analyzedby STEM and EDX. As a result, it was found that the oxidized layerhaving a thickness of about 1.5 nm measured from the surface of thephase-shift film 2 was formed. For this phase-shift film 2, aspectroscopic ellipsometer (manufactured by J.A.Woollam; M-2000D) wasused to measure the optical properties. As a result, at a wavelength of193 nm, a refractive index n was 2.56, and the extinction coefficient kwas 0.65. Also for the phase-shift film 2, the transmittance and phasedifference at a wavelength of the ArF excimer laser light (193 nm) weremeasured by a phase-shift amount measuring device. As a result, thetransmittance was 6.02%, and the phase difference was 177.7 degrees.

Then, the transparent substrate 1 was placed in the single-wafer DCsputtering device, a chromium (Cr) target was used, and the reactivesputtering (DC sputtering) in the mixed gas atmosphere of argon (Ar),nitrogen (N₂), carbon dioxide (CO₂), and helium (He) was conducted, suchthat the etching stopper film 3 made of chromium, oxygen, carbon, andnitrogen (CrOCN film: Cr: 48.9 at %, O: 26.4 at %, C: 10.6 at %, N: 14.1at %) and having a film thickness of 5 nm was formed adjacent to thesurface of the phase-shift film 2. The composition of the CrOCN film wasobtained as a result from Auger electron spectroscopy (AES). The samecan be said for the other films below.

Then, the transparent substrate 1 was placed in the single-wafer DCsputtering device, a mixed target of molybdenum (Mo) and silicon (Si)(Mo:Si=21 at % :79 at %) was used, and the reactive sputtering (DCsputtering) in a mixed gas atmosphere of argon (Ar) and helium (He) wasperformed, such that the lower layer of the light-shielding film 4, madeof molybdenum and silicon (MoSi film: Mo: 20.3 at %, Si: 79.7 at %) andhaving a film thickness of 15 nm, was formed adjacent to the surface ofthe etching stopper film 3. Next, the transparent substrate 1 was placedin the single-wafer DC sputtering device, a mixed target of molybdenum(Mo) and silicon (Si) (Mo:Si=4 at %:96 at %) was used, and the reactivesputtering (DC sputtering) in a mixed gas atmosphere of argon (Ar),oxygen (O₂), nitrogen (N₂), and helium (He) was performed, such that theupper layer of the light-shielding film 4, made of molybdenum, silicon,oxygen, and nitrogen (MoSiON film: Mo: 2.6 at %, Si: 57.1 at %, 0:15.9at %, N:24.4 at %) and having a film thickness of 10 nm, was formedadjacent to a surface of the lower layer of the light-shielding film 4.The total film thickness of the light-shielding film 4 was 25 nm.

For the laminated film comprised of the phase-shift film 2, etchingstopper film 3, and light-shielding film 4 laminated on the transparentsubstrate 1, the spectroscopic ellipsometer (manufactured byJ.A.Woollam: M-2000D) was used to measure optical density (OD) withrespect to the light at a wavelength of 193 nm, and it was confirmed tobe 3.03.

Then, the transparent substrate 1 was placed in the single-wafer DCsputtering device, a chromium (Cr) target was used, and the reactivesputtering (DC sputtering) in a mixed gas atmosphere of argon (Ar),nitrogen(N₂), carbon dioxide (CO₂), and helium (He) was performed, suchthat the hard mask film 5 made of chromium, oxygen, carbon, and nitrogen(CrOCN film: Cr: 48.9 at %, O: 26.4 at %, C: 10.6 at %, N: 14.1 at %)and having a film thickness of 15 nm was formed adjacent to the surfaceof the light-shielding film 4. The predetermined cleaning process wasfurther conducted, such that the mask blank 10 of Example 1 wasobtained.

[Manufacture of Phase-Shift Mask]

Then, the mask blank 10 of Example 1 was used to manufacture thephase-shift mask 20 of Example 1 through the following procedure. First,the first resist film having a film thickness of 80 nm and made of achemically amplified resist for electron beam drawing was formedadjacent to the surface of the hard mask film 5 through a spin coatingmethod. Then, a first pattern was drawn with an electron beam on thefirst resist film, and the predetermined development and cleaningprocesses were conducted, such that a first resist film (first resistpattern) 6 a having the first pattern was formed (FIG. 3(a)). The firstpattern included, in a transfer pattern forming region (inner region of132 mm x 104 mm), a transfer pattern of DRAM hp32 nm generation (a finepattern including SRAF with a line width of 40 nm) to be formed in thephase-shift film 2, and further included the alignment mark patternarranged in the region outside the transfer pattern forming region,where the light-shielding band is formed (region where thelight-shielding film 4 is left upon the completion of the phase-shiftmask).

Next, the dry etching with a mixed gas of chlorine and oxygen using thefirst resist pattern 6 a as a mask was performed on the hard mask film5, such that the hard mask film (hard mask film pattern) 5 a having thefirst pattern was formed (FIG. 3(b)). After that, the first resistpattern 6 a was removed.

Next, the dry etching with the fluorine-based gas (CF₄) using the hardmask film pattern 5 a as a mask was performed on the light-shieldingfilm 4, such that the light-shielding film (light-shielding filmpattern) 4 a having the first pattern was formed (FIG. 3(c)).

Next, the dry etching with the mixed gas of chlorine and oxygen usingthe light-shielding film pattern 4 a as a mask was performed, such thatthe etching stopper film (etching stopper film pattern) 3 a having thefirst pattern was formed (FIG. 3(d)). At this time, while the hard maskfilm pattern 5 a was also etched from the surface with the mixed gas ofchlorine and oxygen, it was left, having the thickness of about 5 nm.

Then, the second resist film having the film thickness of 80 nm and madeof the chemically amplified resist for electron beam drawing was formedadjacent to the surface of the hard mask film pattern 5 a through thespin coating method. Subsequently, the second pattern was drawn with theelectron beam on the second resist film, and the predetermineddevelopment and cleaning processes were conducted, such that the secondresist film (second resist pattern) 7 b having the second pattern wasformed. The second pattern comprises the light-shielding band patternarranged in the region outside the transfer pattern forming region.

Next, the dry etching with the mixed gas of chlorine and oxygen usingthe second resist pattern 7 b as a mask was performed, such that thehard mask film (hard mask film pattern) 5 b having the second patternand alignment mark pattern was formed (FIG. 3(e)). After that, thesecond resist pattern 7 b was removed.

Then, the dry etching with the etching gas containing the fluorine-basedgas (SF₆+He) using the etching stopper film pattern 3 a as a mask wasperformed, such that the phase-shift film (phase-shift film pattern) 2 ahaving the first pattern was formed. Further, at the same time, the hardmask film pattern 5 b was used as a mask, so as to form thelight-shielding film (light-shielding film pattern) 4 b having thesecond pattern and alignment mark pattern (FIG. 3(f)).

Next, the dry etching with the mixed gas of chlorine and oxygen usingthe light-shielding film pattern 4 b as a mask was performed, such thatthe etching stopper film (etching stopper film pattern) 3 b having thesecond pattern and alignment mark pattern was formed. At the same time,the hard mask film pattern 5 b was removed as a whole by this dryetching. After that, the predetermined cleaning was conducted, such thatthe phase-shift mask 20 was obtained (FIG. 3(g)).

[Verification Experiment for ArF Light Fastness]

A verification experiment for the ArF light fastness was conducted onthe manufactured phase-shift mask 20 of Example 1. The ArF excimer laserwas irradiated from the transparent substrate 1 side with respect to twoportions on the phase-shift mask 20 of Example 1, in particular, theportion where only the phase-shift film pattern 2 a existed within thetransfer pattern forming region, and the portion where the phase-shiftfilm pattern 2 a, etching stopper film pattern 3 b, and light-shieldingfilm pattern 4 b were laminated within a region wherein thelight-shielding band was formed. The ArF excimer laser was irradiatedintermittently, which was the condition close to the actual exposure byan exposure apparatus.

The specific conditions of the ArF excimer laser irradiation was asfollows: emission frequency: 500 [Hz]; energy density per pulse: 10[mJ/(cm² ·pulse)]; the number of pulses sequentially emitted: 10; timerequired to sequentially emit 10 pulses: 20 [msec]; pulse width: 5[nsec]; idle period after sequential emission (interval period): 500[msec]. Under these irradiation conditions, intermittent irradiation wasperformed for 15 hours. An accumulated exposure amount for the thin filmintermittently irradiated is 10 [kJ/cm²]. During the ArF excimer laserirradiation, the phase-shift mask was placed in the atmosphere at arelative humidity of 35% RH.

Before and after the irradiation of the ArF excimer laser, the patternwidth of the phase-shift film pattern 2 a and the pattern width of thelight-shielding film pattern 4 b at the portion irradiated were measuredto calculate an amount of change in line width before and after the ArFexcimer laser irradiation. As a result, the amount of change in linewidth of the phase-shift film pattern 2 a was 2.2 nm, and sufficientlyhigh ArF light fastness could be confirmed. The amount of change in linewidth of the light-shielding film pattern 4 a was 3.9 nm, andsufficiently high ArF light fastness could be also confirmed.

[Evaluation of Pattern Transfer Performance]

Using AIMS193 (manufactured by Carl Zeiss), a simulation of a transferimage in the exposure transfer to the resist film on a semiconductordevice with the exposure light at the wavelength of 193 nm was performedon the phase-shift mask 20 of Example 1 after the verificationexperiment for the ArF light fastness. As a result of inspection of thetransfer image exposed in this simulation, there was no short ordisconnection in patterns, which satisfied the design specificationsufficiently. From this result, a circuit pattern finally formed on thesemiconductor device may have great accuracy, even if the phase-shiftmask of Example 1 is set on the mask stage of the exposure apparatus toperform the exposure transfer to the resist film on the semiconductordevice. Also, as for the contrast of the alignment mark, there was nomisregistration between the phase-shift film pattern 2 a, etchingstopper film pattern 3 b, and light-shielding film pattern 4 b, and ahigh contrast with respect to the detection light from the alignmentmark detector was obtained.

Example 2 [Manufacture of Mask Blank]

The transparent substrate 1 was prepared by a procedure similar toExample 1. Next, the transparent substrate 1 was placed in thesingle-wafer DC sputtering device, a mixed target of molybdenum (Mo) andsilicon (Si) (Mo:Si=4 at % :96 at %) was used, and the reactivesputtering (RF sputtering) in the mixed gas atmosphere of argon (Ar),nitrogen (N₂), and helium (He) was conducted, such that the phase-shiftfilm 2 made of molybdenum, silicon, and nitrogen (MoSiN film) and havinga film thickness of 67 nm was formed on the transparent substrate 1.

Then, on the transparent substrate 1 with the phase-shift film 2 formedthereon, a heat treatment was performed so as to reduce film stress ofthe phase-shift film 2 and to form an oxidized layer on a surface layer.In particular, a heating furnace (electric furnace) was used to conductthe heat treatment at a heating temperature of 450° C. in the air forone hour. For the phase-shift film 2 after the heat treatment, thetransmittance and phase difference at a wavelength of the ArF excimerlaser light (about 193 nm) were measured by the phase-shift amountmeasuring device. As a result, the transmittance was 6.2%, and the phasedifference was 179.5 degrees.

For the phase-shift film 2 after the heat treatment, the measurement wasmade by X-ray photoelectron spectroscopy (XPS). As a result, it wasfound that the oxidized layer (surface layer) having a thickness ofabout 2 nm measured from the surface of the phase-shift film 2 wasformed. It was also found that the layers other than the surface layerin the phase-shift film 2 after the heat treatment were MoSiN(Mo:Si:N=1.8 at %:53.1 at %:45.1 at %).

In the X-ray photoelectron spectroscopy for the phase-shift film 2 ofExample 2, montage spectrum was derived at each depth from the filmsurface. From the results of montage spectra, it was found that thephase-shift film 2 of Example 2 contained a relatively larger number ofMo—Si bonds than Mo—N bonds as the internal bonding states. In view ofthese results, the phase-shift film 2 of Example 2 is an incompletenitride film.

Subsequently, the etching stopper film 3, light-shielding film 4, andhard mask film 5 were formed in said order adjacent to the surface ofthe phase-shift film 2 by a procedure similar to Example 1. Thepredetermined cleaning process was further conducted, such that the maskblank 10 of Example 2 was obtained. Before forming the hard mask film 5,the spectroscopic ellipsometer (manufactured by J.A.Woollam: M-2000D)was used with respect to the laminated film comprised of the phase-shiftfilm 2, etching stopper film 3, and light-shielding film 4 laminated onthe transparent substrate 1, so as to measure the optical density (OD)in relation to the light at a wavelength of 193 nm, and it was confirmedto be 3.01.

[Manufacture of Phase-Shift Mask]

The mask blank 10 of Example 2 was used to manufacture the phase-shiftmask 20 of Example 2 through a procedure similar to Example 1.

[Verification Experiment for ArF Light Fastness]

A verification experiment for the ArF light fastness was conducted onthe manufactured phase-shift mask 20 of Example 2 through a proceduresimilar to Example 1. As a result, the amount of change in line width ofthe phase-shift film pattern _a before and after the irradiation of theArF excimer laser was 2.7 nm, and sufficiently high ArF light fastnesscould be confirmed. The amount of change in line width of thelight-shielding film pattern 4 a before and after the irradiation of theArF excimer laser was 3.9 nm, and sufficiently high ArF light fastnesscould also be confirmed.

[Evaluation of Pattern Transfer Performance]

Using AIMS193 (manufactured by Carl Zeiss), a simulation of a transferimage in the exposure transfer to the resist film on a semiconductordevice with the exposure light at the wavelength of 193 nm was performedon the phase-shift mask 20 of Example 2 after the verificationexperiment for the ArF light fastness. As a result of inspection of thetransfer image exposed in this simulation, there was no short ordisconnection in patterns, which satisfied the design specificationsufficiently. From this result, a circuit pattern finally formed on thesemiconductor device may have great accuracy, even if the phase-shiftmask of Example 2 is set on the mask stage of the exposure apparatus toperform the exposure transfer to the resist film on the semiconductordevice. Also, as for the contrast of the alignment mark, there was nomisregistration between the phase-shift film pattern 2 a, etchingstopper film pattern 3 b, and light-shielding film pattern 4 b, and ahigh contrast with respect to the detection light from the alignmentmark detector was obtained.

Example 3 [Manufacture of Mask Blank]

The transparent substrate 1 was prepared by a procedure similar toExample 1. Next, the transparent substrate 1 was placed in thesingle-wafer RF sputtering device, a silicon (Si) target was used, andthe reactive sputtering (RF sputtering) using the mixed gas of argon(Ar) and nitrogen (N₂) (flow ratio: Ar:N₂=2:3, pressure=0.035 Pa) as asputtering gas at a power of RF power supply of 2.8 kW was conducted,such that the low-transmittance layer 221 made of silicon and nitrogen(Si:N=59 at %:41 at %) and having a thickness of 12 nm was formed on thetransparent substrate 1.

Only the low-transmittance layer 221 was formed on a main surface ofanother transparent substrate under the same conditions, and thespectroscopic ellipsometer (manufactured by J.A.Woollam: M-2000D) wasused to measure the optical properties of this low-transmittance layer221. As a result, at a wavelength of 193 nm, the refractive index n was1.85, and the extinction coefficient k was 1.70. As for the conditionsused to form the low-transmittance layer 221, the film formingconditions such as a flow ratio at which the film may be stably formedin the area of metal mode was selected after the verification of arelationship between a flow ratio of N₂ gas in the mixed gas of Ar gasand N₂ gas as the sputtering gas and a deposition rate by thesingle-wafer RF sputtering device used. The composition of thelow-transmittance layer 221 was obtained as a result from themeasurement by X-ray photoelectron spectroscopy (XPS). The same can besaid for the other films below.

Next, the transparent substrate 1 with the low-transmittance layer 221laminated was placed in the single-wafer RF sputtering device, a silicon(Si) target was used, and the reactive sputtering (RF sputtering) usingthe mixed gas of argon (Ar) and nitrogen (N₂) (flow ratio: Ar:N₂=1:3,pressure=0.09 Pa) as a sputtering gas at a power of RF power supply of2.8 kW was conducted, such that the high-transmittance layer 222 made ofsilicon and nitrogen (Si:N=46 at % :54 at %) and having a thickness of55 nm was formed on the low-transmittance layer 221. Only thehigh-transmittance layer 222 was formed on a main surface of anothertransparent substrate under the same conditions, and the spectroscopicellipsometer (manufactured by J.A.Woollam: M-2000D) was used to measurethe optical properties of this high-transmittance layer 222. As aresult, at a wavelength of 193 nm, the refractive index n was 2.52, andthe extinction coefficient k was 0.39. As for the conditions used toform the high-transmittance layer 222, the film forming conditions suchas a flow ratio at which the film may be stably formed in the area ofreactive mode (poison mode) was selected after the verification of arelationship between a flow ratio of N₂ gas in the mixed gas of Ar gasand N₂ gas as the sputtering gas and a deposition rate by thesingle-wafer RF sputtering device used.

Next, the transparent substrate 1 with the low-transmittance layer 221and high-transmittance layer 222 laminated was placed in thesingle-wafer RF sputtering device, a silicon (Si) target was used, andthe reactive sputtering (RF sputtering) using the mixed gas of argon(Ar) and nitrogen (N₂) (flow ratio: Ar:N₂=1:3, pressure=0.09 Pa) as asputtering gas at a power of RF power supply of 2.8 kW was conducted,such that the uppermost layer 223 having a thickness of 4 nm was formedon the high-transmittance layer 222. Further, the oxidation treatmentusing ozone was conducted on the uppermost layer 223, such that anoxidized layer was formed on a surface layer of the uppermost layer 223.Thus, the uppermost layer 223 became a compositional gradient film whichhad the oxygen content increasing with distance from the transparentsubstrate 1.

Through the above procedure, the phase-shift film 2 comprised of thelow-transmittance layer 221, high-transmittance layer 222, and uppermostlayer 223 was formed on the transparent substrate 1. For the phase-shiftfilm 2, the transmittance and phase difference at a wavelength of theArF excimer laser light (about 193 nm) were measured by the phase-shiftamount measuring device. As a result, the transmittance was 5.97%, andthe phase difference was 177.7 degrees.

Then, the etching stopper film 3, light-shielding film 4, and hard maskfilm 5 were formed in said order adjacent to the surface of thephase-shift film 2 by a procedure similar to Example 1. Thepredetermined cleaning process was further conducted, such that the maskblank 102 of Example 3 was obtained. Before forming the hard mask film5, the spectroscopic ellipsometer (manufactured by J.A.Woollam: M-2000D)was used for the laminated film comprised of the phase-shift film 2,etching stopper film 3, and light-shielding film 4 laminated on thetransparent substrate 1, so as to measure the optical density (OD) inrelation to the light at a wavelength of 193 nm, and it was confirmed tobe 3.06.

[Manufacture of Phase-Shift Mask]

The mask blank 102 of Example 3 was used to manufacture the phase-shiftmask 20 of Example 3 through a procedure similar to Example 1.

[Verification Experiment for ArF Light Fastness]

A verification experiment for the ArF light fastness was conducted onthe manufactured phase-shift mask 20 of Example 3 through a proceduresimilar to Example 1. As a result, the amount of change in line width ofthe phase-shift film pattern 2 a before and after the irradiation of theArF excimer laser was 1.0 nm, and sufficiently high ArF light fastnesscould be confirmed. The amount of change in line width of thelight-shielding film pattern 4 a before and after the irradiation of theArF excimer laser was 3.9 nm, and sufficiently high ArF light fastnesscould also be confirmed.

[Evaluation of Pattern Transfer Performance]

Using AIMS193 (manufactured by Carl Zeiss), a simulation of a transferimage in the exposure transfer to the resist film on a semiconductordevice with the exposure light at the wavelength of 193 nm was performedon the phase-shift mask 20 of Example 3 after the verificationexperiment for the ArF light fastness. As a result of inspection of thetransfer image exposed in this simulation, there was no short ordisconnection in patterns, which satisfied the design specificationsufficiently. From this result, a circuit pattern finally formed on thesemiconductor device may have great accuracy, even if the phase-shiftmask of Example 3 is set on the mask stage of the exposure apparatus toperform the exposure transfer to the resist film on the semiconductordevice. Also, as for the contrast of the alignment mark, there was nomisregistration between the phase-shift film pattern 2 a, etchingstopper film pattern 3 b, and light-shielding film pattern 4 b, and ahigh contrast with respect to the detection light from the alignmentmark detector was obtained.

REFERENCE NUMERALS

1: transparent substrate

2, 22: phase-shift film

2 a: phase-shift film pattern

3: etching stopper film

3 a, 3 b: etching stopper film pattern

4: light-shielding film

4 a, 4 b: light-shielding film pattern

5: hard mask film

5 a, 5 b: hard mask film pattern

6 a: first resist pattern

7 b: second resist pattern

10, 102: mask blank

20: phase-shift mask

221: low-transmittance layer

222: high-transmittance layer

223: uppermost layer (surface layer)

What is claimed is:
 1. A mask blank having a structure in which aphase-shift film, an etching stopper film, a light-shielding film, and ahard mask film are laminated in said order on a transparent substrate,wherein the hard mask film is made of a material containing chromium;wherein the phase-shift film is made of a material in which transitionmetal, silicon, and nitrogen are contained, and a ratio of the content[atom %] of transition metal to the total content [atom %] of transitionmetal and silicon is less than 4 [%]; wherein the light-shielding filmhas a single layer structure, or a laminated structure comprised ofmultiple layers; and wherein at least one layer in the light-shieldingfilm is made of a material which contains transition metal and silicon,but does not contain nitrogen and oxygen, or a material which containstransition metal, silicon, and nitrogen, and satisfies the conditions ofFormula (1) below:C _(N)≤9.0×10⁻⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³−7.718×10⁻² ×R _(M)²+3.611×R _(M)−21.084   Formula (1) wherein R_(M) is a ratio [%] of thecontent [atom %] of transition metal to the total content [atom %] oftransition metal and silicon in said one layer, and C_(N) [atom %] isthe content [atom %] of nitrogen in said one layer.
 2. The mask blankaccording to claim 1, wherein the phase-shift film has a function oftransmitting ArF excimer laser light at a transmittance of 1% or moreand 30% or less.
 3. The mask blank according to claim 1, wherein theoptical density with respect to ArF excimer laser light is 2.7 or morein the laminated structure of the phase-shift film, the etching stopperfilm, and the light-shielding film.
 4. A phase-shift mask manufacturedfrom the mask blank according to claim
 1. 5. A method for manufacturinga semiconductor device, comprising the step of: setting the phase-shiftmask according to claim 4 on an exposure apparatus having an exposurelight source for emitting ArF excimer laser light, so as to transfer atransfer pattern onto a resist film formed on a transfer targetsubstrate.
 6. A mask blank having a structure in which a phase-shiftfilm, an etching stopper film, a light-shielding film, and a hard maskfilm are laminated in said order on a transparent substrate, wherein thehard mask film is made of a material containing chromium; wherein thephase-shift film is comprised of a surface layer and layers other thanthe surface layer; wherein the layers other than the surface layer aremade of a material in which transition metal, silicon, and nitrogen arecontained, a ratio of the content [atom %] of transition metal to thetotal content [atom %] of transition metal and silicon is less than 9[%], and the material is incomplete nitride; wherein the light-shieldingfilm has a single layer structure, or a laminated structure comprised ofmultiple layers; and wherein at least one layer in the light-shieldingfilm is made of a material which contains transition metal and silicon,but does not contain nitrogen and oxygen, or a material which containstransition metal, silicon, and nitrogen, and satisfies the conditions ofFormula (1) below:C _(N)≤9.0×10⁻⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³−7.718×10² ×R _(M)²+3.611×R _(M)−21.084   Formula (1) wherein R_(M) is a ratio [%] of thecontent [atom %] of transition metal to the total content [atom %] oftransition metal and silicon in said one layer, and C_(N) [atom %] isthe content [atom %] of nitrogen in said one layer.
 7. The mask blankaccording to claim 6, wherein the phase-shift film has a function oftransmitting ArF excimer laser light at a transmittance of 4% or moreand 9% or less.
 8. The mask blank according to claim 6, wherein theoptical density with respect to ArF excimer laser light is 2.7 or morein the laminated structure of the phase-shift film, the etching stopperfilm, and the light-shielding film.
 9. A phase-shift mask manufacturedfrom the mask blank according to claim
 6. 10. A method for manufacturinga semiconductor device, comprising the step of: setting the phase-shiftmask according to claim 9 on an exposure apparatus having an exposurelight source for emitting ArF excimer laser light, so as to transfer atransfer pattern onto a resist film formed on a transfer targetsubstrate.
 11. A mask blank having a structure in which a phase-shiftfilm, an etching stopper film, a light-shielding film, and a hard maskfilm are laminated in said order on a transparent substrate, wherein thehard mask film is made of a material containing chromium; wherein thephase-shift film is comprised of a surface layer and layers other thanthe surface layer; wherein the layers other than the surface layer aremade of a material consisting of silicon and nitrogen, or a materialconsisting of silicon, nitrogen, and one or more elements selected frommetalloid elements, non-metallic elements, and noble gases; wherein thesurface layer of the phase-shift film is made of a material consistingof silicon, nitrogen, and oxygen, or a material consisting of silicon,nitrogen, oxygen, and one or more elements selected from metalloidelements, non-metallic elements, and noble gases; wherein thelight-shielding film has a single layer structure, or a laminatedstructure comprised of multiple layers; and wherein at least one layerin the light-shielding film is made of a material which containstransition metal and silicon, but does not contain nitrogen and oxygen,or a material which contains transition metal, silicon, and nitrogen,and satisfies the conditions of Formula (1) below:C _(N)≤9.0×10⁻⁶ ×R _(M) ⁴−1.65×10⁻⁴ ×R _(M) ³'7.718×10² ×R _(M)²+3.611×R _(M)−21.084   Formula (1) wherein R_(M) is a ratio [%] of thecontent [atom %] of transition metal to the total content [atom %] oftransition metal and silicon in said one layer, and C_(N) [atom %] isthe content [atom %] of nitrogen in said one layer.
 12. The mask blankaccording to claim 11, wherein the phase-shift film has a function oftransmitting ArF excimer laser light at a transmittance of 1% or moreand 30% or less.
 13. The mask blank according to claim 11, wherein thelayers other than the surface layer in the phase-shift film have astructure in which a low-transmittance layer and a high-transmittancelayer are laminated, and wherein the low-transmittance layer hasnitrogen content that is relatively lower than the high-transmittancelayer.
 14. The mask blank according to claim 11, wherein the opticaldensity with respect to ArF excimer laser light is 2.7 or more in thelaminated structure of the phase-shift film, the etching stopper film,and the light-shielding film.
 15. A phase-shift mask manufactured fromthe mask blank according to claim
 11. 16. A method for manufacturing asemiconductor device, comprising the step of: setting the phase-shiftmask according to claim 15 on an exposure apparatus having an exposurelight source for emitting ArF excimer laser light, so as to transfer atransfer pattern onto a resist film formed on a transfer targetsubstrate.